R Rrand - Universidade do Porto

Wednesday, 3 August 2011 5:16 PM 2_Organic_Petrology_Macerals_Rank 1 

ICCP Training Course on 

Dispersed Organic Matter 

CHAPTER 2 

ORGANIC PETROLOGY, MACERALS, 

MICROLITHOTYPES, 

LITHOTYPES, MINERALS, RANK 

Wednesday September 7- Friday September 9, 2011, 

HELD AT 

Departamento de Geociências, 

Ambiente e Ordenamento do Território, 

Faculdade de Ciências da Universidade do Porto 

Porto, Portugal


CONTENTS 

2. ORGANIC PETROLOGICAL METHODS 

2.1 EARLY STUDIES 4 

2.2 LATER DEVELOPMENTS 5 

2.3 PETROGRAPHIC COMPOSITION OF ORGANIC MATTER 6 

2.3.1 TYPE 6 

TABLE 2.1. BIOCHEMICAL COALIFICATION 7 

2.3.2 THE MACERAL CONCEPT 7 

2.3.3 THE MACERAL GROUPS 8 

TABLE 2.2. MACERAL GROUPS, SUB-GROUPS, MACERALS 

AND SUB-MACERALS 10 

TABLE 2.3. ILLUSTRATION OF MACERAL GROUPS AND 

SOME MACERALS 12 

TABLE 2.4. ILLUSTRATION OF VITRINITE SUB-GROUPS 13 

TABLE 2.5. ILLUSTRATION OF INERTINITE MACERALS 14 

TABLE 2.6. ILLUSTRATION OF LIPTINITE MACERALS 15 

2.3.3.1 THE VITRINITE GROUP 16 

2.3.3.1.1 TELOVITRINITE SUBGROUP 20 

2.3.3.1.2 DETROVITRINITE SUBGROUP 23 

2.3.3.1.3 GELOVITRINITE SUBGROUP 26 

2.3.3.2 THE LIPTINITE GROUP 27 

2.4.1 SPORINITE 28 

TABLE 2.7. CHEMICAL AFFINITIES OF THE LIPTINITE MACERALS. 28 

2.4.2 CUTINITE 29 

2.4.3 SUBERINITE 29 

2.4.4 RESINITE 30 

2.4.5 LIPTODETRINITE 31 

2.4.6 ALGINITE 31 

2.4.7 BITUMINITE 32 

2.4.8 EXSUDATINITE 33 

2.3.3.3 THE INERTINITE GROUP 34 

2.3.3.3.1 GENERAL 34 

2.3.3.3.2 FUSINITE 35 

2.3.3.3.3 SEMIFUSINITE 35 

2.3.3.3.4 INERTODETRINITE 35 

2.3.3.3.5 MACRINITE 36 

2.3.3.3.6 MICRINITE 36 

2.3.3.3.7 FUNGINITE 36 

2.3.3.3.8 SECRETINITE 36 

2.3.4 MICROLITHOTYPES 37 

2.4. COAL RANK - PHYSICO-CHEMICAL COALIFICATION 37 

2.4.1 PROCESSES ASSOCIATED WITH RANK CHANGE 37 

2.4.2 MATURATION CONCEPT 38 

TABLE 2.8. PHYSICO-CHEMICAL COALIFICATION – RANK CHANGE 39 

2.4.3. ORGANIC PETROLOGICAL METHODS 39 

2.4.4. VITRINITE REFLECTANCE 41


2.4.4.1 OPTICAL PROPERTIES OF VITRINITE AND THEIR 

INFLUENCE ON MEASUREMENTS 41 

Table 2.4. Diagram to illustrate the ISO coal classification 11760-2005 42 

Table 2.5 - Low, Medium and High Rank coals 43 

2.4.4.2 RELATIONSHIP OF REFLECTANCE TO 

OTHER OPTICAL PROPERTIES 45 

2.4.5. TECHNIQUES FOR MEASURING VITRINITE REFLECTANCE 47 

2.4.5.1 GENERAL 47 

2.4.5.2 USE OF VARIOUS IMMERSION MEDIA 47 

2.4.5.3 PROPERTIES MEASURED 48 

Table 2.9. Properties measured for vitrinite reflectance. 48 

2.4.5.3.1 MEAN MAXIMUM REFLECTANCE 48 

2.4.5.3.2 RANDOM MEASUREMENTS BUT WITH POLAR 50 

2.4.5.3.3 RANDOM REFLECTANCE 50 

2.4.6. HISTOGRAMS 50 

2.4.7 UNUSUAL TYPE EFFECTS 51 

2.5 CARBONIZATION 52 

FIGURE 2.1 Plates of coals and the conversion to artificial semi-cokes 53 

FIGURE 2.2. Mesophase development in natural bitumen, 54 

FIGURE 2.3. Natural coke. Little Limestone coal, Visean, 54 

FIGURE 2.4. Meta-exsudatinite 55 

2.5. BIBLIOGRAPHY AND REFERENCES 56 

Glossary 59 

APPENDICES. 63 

TABLE A2.1. MAJOR CONSIDERATIONS IN RELATION TO 

VITRINITE REFLECTANCE 63 

TABLE A2.2. SAMPLE REQUIREMENTS FOR VITRINITE REFLECTANCE 64 

TABLE A2.3. METHODS OF MEASUREMENT 65 

TABLE A2.4. INFORMATION IN REFLECTANCE DATA 66 

TABLE A2.5. LATER DEVELOPMENTS 67 

TABLE A2.6. LIMITATIONS AND COMPLICATIONS 68 

TABLE A2.6. COMPLICATIONS 69 

TABLE A2.7. REPRODUCIBILITY DATA FOR SIX COALS 71

2. ORGANIC PETROLOGICAL METHODS 

2.1 EARLY STUDIES 


The first organic petrological studies were undertaken in Britain in the middle part of the 19 th 

century (Murchison, 1978). They relied upon the use of thin sections and none of the 

researchers had any formal training in geology, nor did they practice as geologists, hence the 

title of the 1978 paper by Murchison. The work of Stopes (1919) is commonly taken to mark 

a new phase of interest in coal by geologists and in petrological techniques for studying coal 

but had been in parallel with the use of two relatively difficult and less productive techniques, 

flame etching followed by reflected light microscopy (Winter, 1913; Seyler, 1929) and thin 

section methods (Thiessen, 1920; Lomax, 1925). Flame etching proved useful for studies on 

palaeobotany and thin section methods were developed to a full system permitting analysis of 

coals. The difficulty of making thin sections, the opaque character of some components even 

at low rank and the opacity of medium and high rank coals restricted the usefulness of thin 

section methods. 

Reflected light methods suffered from the low optical contrast between components using air 

immersion (dry) lenses and the high glare from a combination of the early opaque 

illuminators and the low quality of early oil immersion lenses. The German school, working 

closely with the German microscope firms of Leitz and Zeiss succeeded in developing a 

suitable illuminator (the Berek prism) and low glare oil immersion lenses for use in reflected 

light. The realisation that much of the work required only medium power lenses was a critical 

factor in the development of reflected light techniques. 

Images could be obtained with air immersion lenses but with them the contrast between the 

various components within coals is very low. Oil immersion lenses gave sufficient contrast to 

allow resolution in reflected light of the three maceral groups, vitrinite, inertinite and liptinite 

(initially termed exinite). The recognition of these was a logical outcome of Stopes' early 

work on lithotypes and the maceral system was published by her in 1935. Two other tools 

essential to organic petrology were invented in the 1930's and manufactured by Ernst Leitz of 

Wetzlar. 

The development of the six spindle integrating stage and the Berek Photometer, respectively, 

permitted the quantitative assessment of type and rank. Both have been replaced by newer 

instruments (respectively, the point counter and the photomultiplier photometer) that give 

essentially the same information, but much more quickly and accurately. In turn point 

counters and photomultipliers are being replaced by newer methods of determining 

percentages of components and their reflectances. 

Liptinite and some vitrinites show strong or, at least, distinct autofluorescence when 

irradiated with ultraviolet, violet or blue light. Illumination of samples in fluorescence-mode


provides invaluable supplementary information to vitrinite reflectance. An excellent recent 

review of the application of all organic petrology techniques to source rock studies is given 

by Teichmüller (1986). 

Organic petrology permits determination of the type and abundance of the organic matter 

occurring as discrete particles at the same time that rank (or level of organic maturation) is 

assessed. Rank and maturation level are normally and most easily assessed from vitrinite 

reflectance but the fluorescence properties of both liptinite and vitrinite can also be used as 

an indicator of rank. Providing that the vitrinite is correctly identified, vitrinite reflectance 

provides the most direct and precise method of rank assessment for most samples. In the 

absence of discrete organic matter, it is possible in some instances to use the fluorescence 

characteristics of the mineral matter to give a general assessment of the level of maturation. 

The terminology used here for organic matter follows, wherever possible, that of the Stopes 

Heerlen System as modified for the ICCP 1994 System. The maceral terms used are shown in 

Table 2.1. 

2.2 LATER DEVELOPMENTS 

Although coal petrological methods were developed initially as a form of scientific 

endeavour they rapidly became oriented to use by the coal industry especially in relation to 

coking. During the period from about 1925 to 1950 the basic terminology for reflected light 

work was developed. At the same time, related methods were developed to study coke 

petrology. 

Early work tended to focus on coal type, largely because of the instrumental difficulties of 

measuring vitrinite reflectance. In many ways this is paradoxical because most studies were 

directed toward the bright coals from the Carboniferous of Europe and the UK. These coals 

show relatively little type variation, but in coalfields such as those in the Ruhr and South 

Wales, rank variation is very large. 

Most of the work to initially establish rank variation within the Carboniferous was done using 

chemical analyses. Much of this work remained unpublished and concepts of the spatial 

distribution of coal rank remained little advanced over those stated by Hilt in the previous 

Century. After 1946, the National Coal Board in the UK published the rank maps that arose 

from the work of the DSIR prior to 1939. 

Around 1960 it was recognised that vitrinite reflectance could be applied to the study of rank 

variation in the thick sequences within sedimentary basins that were of interest to oil 

companies. At first measurements were restricted to coals, but gradually were extended to 

vitrinite occurring in associated clastics and then all types of sequences where vitrinite can 

occur. This includes most marine sequences, although vitrinite is commonly only a minor 

component of most marine organic matter assemblages.


At the same time it was recognised that the maceral system that had been developed for coals 

could be applied with minor changes and extensions, to the organic matter in all post-Silurian 

sequences. These extensions lead to a change in name for the study of organic matter by 

petrological methods from coal petrology to organic petrology. This newer term also 

embraces coke petrology as well as the petrology of organic matter in rocks other than coal. 

Vitrinite is not present in sequences that are Silurian, or older, because land plants had not yet 

evolved. However, the remains of graptolites and chitinozoans provide a substitute for 

vitrinite in rocks of Silurian, Ordovician and Middle and Upper Cambrian age. Alginite is 

present back into the Precambrian and where these are at low levels of maturation, 

fluorescence properties can be used to assess maturation levels. Additionally, many 

occurrences of lamalginite develop measurable reflectances and these can be used to assess 

maturation even if they cannot be directly correlated with vitrinite reflectance. Bitumen 

reflectances can also be used, so that it is possible to use organic petrology techniques for 

rocks of Precambrian age. 

Organic petrology studies for the oil industry greatly increase the range of rank or maturity 

that are commonly studied. The coal industry is still dominated by production of coals of 

bituminous rank although coals of higher and lower rank are also mined. Even within this 

rank range, the coal industry is dominated by coals of medium to low bituminous rank. By 

contrast, many studies for petroleum span a range from low rank brown coals to metaanthracite. 

The development of exploration for shale gas has placed a marked emphasis on 

exploration of sedimentary sections lying within the anthracitic range of rank. 

Extension of the techniques to oil industry studies has resulted in a need to develop the 

techniques to cope with a much greater range of vitrinite types and to treat a very wide range 

of rank as a normal outcome. It has also lead to a greater understanding of the three 

dimensional distribution of rank within sedimentary basins. Modelling of maturation, has 

also lead to an understanding of the timing of coalification. Techniques such as apatite 

fission track analysis (AFTA�) provide directly determined data on the timing of some 

specific temperature markers. Integration of various types of data has also become extremely 

important. 

2.3 PETROGRAPHIC COMPOSITION OF ORGANIC MATTER 

2.3.1 TYPE 

Type is determined by the vegetation and the nature of plant, and to a lesser extent animal 

material contributed to the sediment and to the extent of early diagenetic alteration. This 

early digenetic alteration has been most intensively studied in relation to peat. Organic 

matter type is described in terms of the entities that can be distinguished with an optical 

microscope.


Recognition of type is commonly traced back to the definition of lithotypes in coals by 

Stopes in 1919, although in practice many distinctions had been made on the basis of coal 

type factors for most of the history of coal – for example the recognition of cannel coals. 

In the Stopes system, vitrain relates to thick layers of coal largely composed of what became 

recognised as vitrinite and fusain to a particular assemblage of fusinite and semifusinite. 

Durain is a dull coal dominated by macrinite and sporinite and clarain a coal lying in 

composition between vitrain and durain. In practice, the Stopes lithotype system is either not 

appropriate to many coals other than the Carboniferous coals of the UK (on which it was 

based) or does not provide much discrimination. For example, Tertiary coals tend to show 

relatively few differences at the lithotype scale. 

TABLE 2.1. BIOCHEMICAL COALIFICATION 

INITIAL MATERIAL 

Oxygen potential 

PROCESS RESPONSE 

Aerobic 

COMPOUND GROUPS 

aerobic to anaerobic Anaerobic 

Proteins strong degradation hydrolysis to monomers 

Carbohydrates some degradation}followed 

by repolymerisation 

to humic acids to brown coal* 

Lignin degradation but preservation 

after repolymerization 

to humic acids to brown coal* 

Lipids cuticles and lipoid 

coatings, resins spores and 

pollens 

Plant material HUMIFICATION 

(BURIAL AND TIME) 

2.3.2 THE MACERAL CONCEPT 

virtually unaltered report to peat and brown coal* 

PEAT* ___ > BROWN COAL* 

Dispersed organic matter 

Fluids produced H2O, H2S, CO2 CH4 

Coal is not homogeneous under the optical microscope and it can be seen to consist of a 

number of constituents. These are termed macerals (Stopes, 1935) and are distinguished on 

the basis of morphology, optical properties and some other properties such as polishing 

hardness. An analogy is commonly made for macerals with the relationship of minerals to


rocks of inorganic origin. The analogy is not complete because whereas minerals have a 

distinct composition (or range), coal macerals range widely in their composition and physical 

properties even in coals of one level of rank and the properties of macerals vary 

systematically with rank. It should also be noted that minerals are crystalline whereas 

macerals exhibit form anisotropy over most of the rank range and develop crystalline 

structures only at high rank or where heating to coke has occurred. The presence of form 

anisotropy becomes an important topic of study where vitrinite bireflectance is studied. 

Most coals have a heterogeneous structure that is visible in hand specimen and a set of 

lithotype terms was introduced to describe the coal types that could be distinguished in hand 

specimen by Stopes (1919). This lithotype system was developed for coals of Carboniferous 

age and the system cannot readily be applied to coals of some other ages (especially the 

Tertiary) because similar differences in hand specimen appearance are not always present. 

Properties at the lithotype level have recently become of greater significance due to the 

increased importance of extraction of coal bed methane. Fracture patterns are important in 

relation to methane production and these are related to the structure of the coals at the 

lithotype level. 

The optical microscope shows a greater level of heterogeneity than is evident in hand 

specimen and although the lithotype system is not readily applied to Tertiary coals, the 

maceral system is applicable to coals of all ages. Studies with electron microscope 

techniques show that heterogeneity persists well beyond the level of resolution of the optical 

microscope. In practical terms the optical microscope represents the limit of useful 

resolution for most studies. 

Maceral recognition is dependent primarily upon the morphology and secondarily on the 

optical properties of the entities. Distinction of macerals under the microscope is made by 

considering the morphology, internal texture and polishing relief (polishing relief is assessed 

against adjacent components) and the optical properties, especially the reflectance. To 

attempt to minimise ambiguity in descriptions and terminology, standard rules have been 

established to define conditions for examination of samples. Samples should be polished 

with some, but not excessive relief, and examined in oil of 1.518 refractive index, using a low 

glare optical system with objectives in the range of nominal magnification of 25 to 50x. 

Morphology is the prime criterion for the distinction of the macerals but reflectance is a very 

important adjunct and in some circumstances may become the determining property. 

Studies on maceral concentrates show that each maceral has a range of composition at any 

given rank and that all of the macerals show systematic changes in properties with rank. 

Many of the shapes and structures observed within macerals can be related to specific plant 

organs and plant genera and species. 

The maceral system developed for coals is directly applicable to organic matter in other types 

of sedimentary rocks. While organic petrology can, in theory, be applied to organic matter in


rocks other than coals, it is very desirable that persons wishing to study organic matter in 

other rocks first become familiar with both maceral analysis and vitrinite reflectance 

measurement for coals, desirably for coals from a wide range of age and rank. In particular, 

an understanding of the nature of normal populations of inertinite and vitrinite in single coals 

forms a highly desirable background to the recognition of these maceral groups in other types 

of rocks. 

2.3.3 THE MACERAL GROUPS 

All maceral names have the suffix 'inite' and an hierarchy has been established of maceral 

groups, macerals and sub-macerals. Three maceral groups are recognized: 

VITRINITE LIPTINITE (FORMERLY EXINITE) INERTINITE 

Each maceral group includes macerals that have affinities in origin or similarities in 

properties. Similarities in origin include both botanical affinities and the mode of 

preservation within the sediment. The ICCP maceral classification is given in Table 2.1 and 

some categories are illustrated in Table 2.2 

A small number of terms additional to those developed from a study of coal are required to 

encompass the additional types of organic matter preserved in non-coal lithologies. 

Otherwise the maceral terminology developed for coal seams provides a workable basis for 

classifying discrete particles of organic matter in non-coal lithologies. Further, most of the 

concepts developed in relation to coals can be applied at least in part to the organic matter in 

other rock types. 

The three maceral groups show differences in their chemical composition. Isometamorphic 

coals are defined as those having the same history of temperature and pressure over time. 

For coals that are isometamorphic with those having a vitrinite carbon content of 84%, the 

hydrogen content averages about 7% in the liptinite macerals, about 5.5% in the vitrinite and 

less than about 4.0% in the inertinite. Corresponding volatile matter yields are about 75% for 

liptinite, 35% for the vitrinite and about 20 to 25% for the inertinite. 

The content of aliphatic hydrogen is much higher in liptinite than in vitrinite. Oxygen 

contents tend to be higher in inertinite than in vitrinite and the oxygen tends to be more 

firmly bound in the inertinite than in the vitrinite. In vitrinite at low ranks, the carbon atoms 

are approximately evenly divided between aliphatic and aromatic bonding, but the hydrogen 

occurs dominantly as aliphatic groupings. With increasing rank, aromaticity increases in all 

of the maceral groups and this results in a convergence of many properties at higher rank. 

At low rank, in reflected white light, liptinite appears dark, vitrinite appears as a mesostasis 

of medium grey appearance and the inertinite has a higher reflectance than the other maceral 

groups. At the coalification jump, the reflectance of the liptinite converges on that of the 

vitrinite. Within the semi-anthracite to anthracite range, the reflectances of vitrinite and 

inertinite converge. However, except in the case of some contact-altered vitrinites, the 

bireflectance of vitrinite is much greater than that of inertinite so that these two maceral

TABLE 2.2. MACERAL GROUPS, SUB-GROUPS, MACERALS AND SUB-MACERALS 


MACERAL GROUP MACERAL SUBGROUP MACERAL MACERAL TYPE 

TEXTINITE TEXTINITE A (dark) & B (light) 

TELOVITRINITE {TEXTO-ULMINITE} TELINITE 

ULMINITE 

COLLOTELINITE 

VITRINITE ATTRINITE 

DETROVITRINITE DENSINITE 

VITRODETRINITE 

COLLODETRINITE 

CORPOHUMINITE PHLOBAPHINITE 

GELOVITRINITE CORPOGELINITE 

GELINITE 

LEVIGELINITE/PORIGELINITE 

Macerals with plant cell structures FUSINITE 

SEMIFUSINITE 

INERTINITE FUNGINITE 

Macerals lacking plant cell structures SECRETINITE 

MACRINITE 

MICRINITE 

Fragmental inertinite INERTODETRINITE 

SPORINITE 

CUTINITE 

SUBERINITE 

RESINITE 

LIPTINITE FLUORINITE 

LIPTODETRINITE 

ALGINITE TELALGINITE 

BITUMINITE 

Strictly a bitumen rather than a maceral EXSUDATINITE 

LAMALGINITE 

NOTE: ICCP does not have a table in this form where vitrinite and huminite classifications are been combined. By using the maceral categories, the discrimination 

within the huminite group is retained without implying that vitrinite and huminite are different maceral groups. This form of terminology is more acceptable to oil 

exploration companies compared with the largely arbitrary division into vitrinite and huminite.


groups can still be distinguished if the stage is rotated using polarised light (plane polarised light or 

with partially crossed polars). 

The relative proportions of the maceral groups determine coal type. The vitrinite reflectance of a 

coal can be taken as a measure of its rank. These two variables are substantially independent, that 

is, they are orthogonal variables. Some degree of interaction occurs because the volume changes 

with rank are different for different macerals. Additionally, some macerals such as exsudatinite and 

micrinite are formed during rank change. Type and rank are independent to the extent that coal type 

does not influence coal rank. It may, however, affect some of the properties that are used to 

estimate coal rank. 

Concepts similar to those of coal type and rank apply to the organic matter in other types of 

sedimentary rocks but it is common in that context to refer to rank-related change as the level of 

maturation and organic matter type is generally assessed in terms of source potential. Maturation is 

commonly stated to be a diagenetic process. However, as the driving factors are temperature and 

time, it is more correctly considered as a metamorphic process, part of organic metamorphism. 

Although reflectance is a major distinguishing feature between the maceral groups, morphological 

differences are of critical factor in defining macerals. Most of the liptinite macerals show botanical 

structures that clearly indicate the origin of these macerals. In vitrinite-rich coals, vitrinite occurs as 

a mesostasis to the other macerals and in medium rank coals is distinguished by plastic behaviour 

adjacent to localised stress fields associated with differential compaction. Inertinite is more brittle 

than vitrinite. Although some plastic flow structures are present in lower reflecting inertinite 

occurrences, they are much less marked compared with those found in vitrinite. The characteristics 

used in making distinctions between maceral groups vary over the rank range. 

Other important properties, such as carbon content, show a correlation with reflectance. Carbon 

content was recognized at an early stage as an important measure of coal rank and from this 

correlation it is clear that vitrinite reflectance can also be used to estimate coal rank. For the 

estimation of rank, the measurement of vitrinite reflectance is a simpler procedure than the 

measurement of carbon content. Further, it does not require corrections for the presence of mineral 

matter and the measurements are made on one maceral group, reducing the variation due to changes 

in the relative abundance of the maceral groups. 

Minerals are excluded from the definition of macerals. However, it must be recognized that a sharp 

distinction cannot always be made. Minerals occurring as particles less than about 0.0005 mm 

(0.5nm) in diameter cannot be resolved with an optical microscope. Additionally, in low rank 

coals, some inorganic compounds are present in the water within the macerals and cations can be 

complexed with the organic matter in the coal. In making maceral analyses, mineral particles that 

can be distinguished are recorded separately. 

Clear distinction between the maceral groups can be made in most cases. However, transitions 

between maceral groups do occur. Such transitions are rarely important volumetrically and present 

the greatest problems with some Permian and Cretaceous coals but do not give rise to problems 

with Tertiary coals. The most difficult aspect of making maceral analyses for coals of Tertiary age, 

is the presence in many coals of very small inclusions of liptinite within the vitrinite and the 

resolution of fine grained liptinite-rich aggregates. Accurate point counting of small entities is more 

difficult than for larger entities.


TABLE 2.3. ILLUSTRATION OF MACERAL GROUPS AND SOME MACERALS 

MACERAL Grp MACERAL/ SUBGRP TYPICAL FIELDS 

VITRINITE 

INERTINITE 

LIPTINITE 

TELOVITRINITE 

Telovitrinite with R vmax 

0.68%, field width 0.22mm 

DETROVITRINITE 

Detrovitrinite with R vmax 

0.45%, field width 0.22 

mm. 

FUSINITE 

SEMIFUSINITE 

Semifusinite and inertodetrinite 

with detrovitrinite , R vmax 

1.23%, Field width 0.22 mm 

FUNGINITE 

INERTODETRINITE 

MACRINITE 

MICRINITE 

SPORINITE 

CUTINITE 

SUBERINITE 

RESINITE 

Cutinite and resinite in Miocene 

coal 

FLUORINITE 


ALGINITE 

BITUMINITE 

EXSUDATINITE*

TABLE 2.4. ILLUSTRATION OF VITRINITE SUB-GROUPS 

MACERAL GRP MACERAL SUBGRP TYPICAL FIELDS 

TELOVITRINITE 

VITRINITE 

Telovitrinite R vmax 

0.40% 

Telovitrinite with R vmax 

0.68%, field width 0.22mm 

R vmax 4.6% Partially 

crossed polars, field width 

0.16mm 

DETROVITRINITE 

Detrovitrinite (densinite) 

with R vmax 0.40%, 

field width 0.18 mm. 

Gelovitrinite 

Collodetrinite 

interbedded with 

inertinite 

Rv 0.89% 

Wednesday, 3 August 2011 5:16 PM 2_Organic_Petrology_Macerals_Rank 13

TABLE 2.5. ILLUSTRATION OF INERTINITE MACERALS 

MACERAL GRP MACERAL TYPICAL FIELDS 

INERTINITE 

FUSINITE 

SEMIFUSINITE 

Semifusinite and 

inertodetrinite with 

detrovitrinite , R vmax 

1.23%, Field width 0.22 

mm 

FUNGINITE 

SECRETINITE 

INERTODETRINITE 

MACRINITE 

MICRINITE 


TABLE 2.6. ILLUSTRATION OF LIPTINITE MACERALS 

MACERAL GRP MACERAL TYPICAL FIELDS 

LIPTINITE 

SPORINITE 

Megaspore 

Carboniferous 

Miospore 

Carboniferous 

CUTINITE 

SUBERINITE 

RESINITE 

Cutinite and resinite in 

Miocene coal 

FLUORINITE 


ALGINITE 

BITUMINITE 

EXSUDATINITE* 



Each maceral group is subdivided into a number of macerals. The macerals have a smaller range of 

properties compared with the parent maceral group. Morphology (external shape and internal 

texture) is the primary feature used in differentiating macerals. Further differentiation of macerals 

into maceral varieties can be made on the basis of lower level differences in morphology. 

For the examination of morphology of the liptinite macerals, the use of fluorescence-mode 

illumination is essential. It may also be valuable for some unusual types of vitrinite. Where point 

counting is undertaken, each field should be examined in both reflected white light mode and 

fluorescence-mode. This is to be preferred over the sequential count method where a reflected 

white light mode count is followed by a fluorescence-mode count. The bituminite figured in Table 

2.4 is from marine rocks, Bituminite in coals remains to be defined. 

The various editions of the Glossary produced by the ICCP have different maceral classifications 

for lower rank coals (essentially brown coals) and for coals of higher rank. The main difference is 

the use of the term "HUMINITE" for the group of entities that is termed "VITRINITE" in coals of 

higher rank. The classification for the liptinite and inertinite groups is the same. For this study, the 

classification recommended accepted at the 1999 meeting of the ICCP is used. In this system, the 

term "VITRINITE" is used for related macerals throughout the rank range. It is subdivided into 

three subgroups and the macerals recognised within these subgroups pick up the textural terms that 

are of significance in studies of brown coals. In maceral analyses, vitrinite can be left undivided, 

subdivided to the subgroup level or divided to the maceral and sub-maceral levels, depending upon 

the requirements for the analyses. Vitrinite textural features will be indicated only if discrimination 

is made at the maceral level. 

2.3.3.1 THE VITRINITE GROUP 

Vitrinite is the most abundant maceral in most, but not all, coals. In some coals of Palaeozoic or 

Mesozoic age, inertinite and more rarely liptinite is the most abundant maceral group. Most coals 

of Tertiary age have a very high content of vitrinite, the only exceptions being some relatively rare 

coals in which resinite or bituminite is unusually abundant. Thus, in volumetric terms, vitrinite is 

the most important maceral. 

Distinguishing features of vitrinite 

Vitrinite is distinguished from the other maceral groups primarily on the basis of its morphology, 

but the morphology of vitrinite in coals varies widely. Other properties of vitrinite are normally 

taken into account when making identifications of specific phytoclasts. Reflectance, dispersion of 

reflectance values about the mean, and autofluorescence properties are important additional criteria 

used in identification. 

Most liptinite macerals of low to medium rank show much stronger autofluorescence than vitrinite 

and this is a further distinguishing feature. Thus, although the distinction of vitrinite from other 

maceral groups in coals is made primarily on morphological grounds, in practice, reflectance is 

commonly the most important criterion used to identify any given field. With dispersed organic 

matter in sediments, reflectance is less reliable in identifying vitrinite. 

At low and medium ranks, vitrinite has a reflectance higher than that of liptinite and lower than that 

of inertinite. It shows negative polishing relief with respect to the other maceral groups and most 

minerals. In the middle and upper parts of the bituminous coal range, liptinite reflectance 

converges on that of vitrinite. Within the anthracite range, the maximum reflectance of vitrinite


converges on that of the macerals of the inertinite group, but the minimum reflectance of vitrinite 

remains less than that of inertinite macerals. 

Bireflectance of vitrinite is low at low ranks but becomes distinct in the middle and upper part of 

the bituminous coal rank range. Within the semi-anthracite, anthracite and meta-anthracite rank 

range, bireflectance becomes high to extreme and is an important distinguishing feature for most 

vitrinites in this rank range. Exceptions occur in some cases where elevated rank is caused by 

contact alteration. Over the whole range of coal rank in any given sample, vitrinite typically shows 

a much lower dispersion of maximum reflectance about the mean than the other maceral groups. 

At low ranks, some vitrinites show autofluorescence related to the original botanical structures. 

This is termed primary fluorescence to distinguish it from (secondary) fluorescence that is 

commonly seen within the lower to middle parts of the bituminous rank range. Primary 

fluorescence is rare at reflectances greater than about 0.4% but some unusual types of woody 

structures retain primary fluorescence up to about 0.7% vitrinite reflectance. 

Secondary fluorescence is believed to be due to the presence of bitumen-related compounds that 

impregnate vitrinite. The amount of n-alkanes in extracts from coals increases markedly with 

increasing rank over the range 0.65% to 0.9% vitrinite reflectance. Changes in the intensity and 

spectral characteristics of vitrinite fluorescence over a range of coal rank can be related to extract 

yields and extract chemistry. 

The appearance of vitrinite is strongly influenced by the plane of section in which it is viewed. In 

sections perpendicular, or strongly oblique, to bedding, most vitrinite occurs as elongate lenses. In 

sections parallel with bedding, particles of vitrinite are commonly more equidimensional and are 

less likely to show rounded outlines. Botanical structure may be seen in such sections so that some 

particles may resemble some types of inertinite in morphology. 

Over the rank range from 1.0% to about 1.8% vitrinite reflectance, the polishing relief of vitrinite 

increases and vitrinite has a greater tendency to fracture in compaction structures. Over this rank 

range, reflectance dispersion (low for vitrinite) becomes an important property in distinguishing 

vitrinite. Where vitrinite reflectance is greater than about 2.0%, the presence of distinct 

bireflectance becomes a major feature for the distinction of vitrinite from inertinite (except in the 

case of some thermally altered rocks). 

ORIGIN OF VITRINITE GROUP MACERALS 

Components similar to all of the vitrinite macerals distinguished in low rank coals can be 

recognized in modern peats. Vitrinite precursors form the major proportion of most modern peats. 

These components are formed from the humification of wood and leaf tissues and other parts of 

plants composed dominantly of cellulose and lignin. In general, lignin-rich tissues are more likely 

to be preserved compared with those rich in cellulose. 

The process of transformation of plant tissues into vitrinite group macerals forms part of the process 

of vitrinite diagenesis. Vitrinite diagenesis in the peat stage is favoured by moist conditions. 

Further stages in vitrinite diagenesis can occur during the processes associated with physicochemical 

coalification. 

The tissues preserved within peats tend to be biased towards coniferous plants rather than 

angiosperms but angiosperm tissues are preserved within peats. The different rates of preservation 

may relate to differences in the chemistry of lignin within these two groups of plants.


Compared with most pre-Tertiary coals, modern peats show a much higher ratio of vitrinite to 

inertinite. The inertinite that is present in modern peats, has a high proportion of fungal sclerotinite 

whereas this component is effectively absent from pre-Tertiary coals. Therefore, Recent peats form 

a good analogue for the origin of the peats that formed Tertiary coals but are less useful as 

analogues for the origin of pre-Tertiary coals. However, the differences seem to relate mainly to the 

origin of inertinite although there are also some systematic differences in the telovitrinite and 

detrovitrinite. 

The maceral group vitrinite originates mainly from the humic-acid fraction of humic substances. 

These are dark-coloured compounds of complex composition and contain the elements carbon, 

oxygen, hydrogen and nitrogen. They possess varying molecular weights and solubilities, have an 

aromatic nucleus and contain hydroxyl (-OH) and carboxyl (-COOH) functional groups. The 

compounds form through mouldering and peatification, with some parts of the process extending 

into the brown-coal stage, chiefly from the lignin and cellulose of plant-cell walls. Besides the 

original materials, the formation and properties of humic acids are dependent on the redox potential 

and pH value of the environment. 

Although the main precursor materials of vitrinite are cellulose, lignins and tannins, the 

incorporation of lipid material into humic matter (and thus into vitrinite) is possible. Alkanes and 

fatty acids (C14-22) are present in extracts of humic and fulvic acids from soils. The distribution of 

n-alkanes and the carbon preference indices are similar to those of microbial hydrocarbons. Most of 

these hydrocarbons are bonded as esters to the humic substances. Thus, vitrinite contains, 

intermixed with the coalified products of humic and fulvic acids, aliphatic material of higher plant 

origin and lipids derived from fungi and bacteria that were active during the decay of the parent 

plant material. These lipids are intermixed at the sub-microscopic level. Resins and suberins are 

also commonly associated with some vitrinites and reflectances of vitrinite and resinite and 

suberinite suggest that transitions from vitrinite to both resinite and suberinite occur. 

It has been assumed by some authors that lignin is the sole precursor of vitrinite (the 'lignin theory'). 

Within the Florida Everglades, large areas of peat are found that have been derived from grasses 

and it is now recognised that, with help from fungi and bacteria, some intermediate compounds 

formed during the decomposition of cellulose and proteins, contribute to the formation of humic 

substances. In addition to lipid rich remains, phenolic metabolic products of micro-organisms are 

built into the humic-acid molecules. Direct evidence of the contribution of cellulose to vitrinite 

formation is the occurrence of chemically recognisable cellulose in some woody tissue in some soft 

brown coals. 

Conifers are usually richer in lignin than deciduous trees and conifer lignin tends to be more 

resistant to degradation compared to that from angiosperms. Along with other factors associated 

with conditions in the peat-forming stage, variations in lignin content and type result in different 

modes of preservation and variations in the optical properties and chemistry of vitrinites. 

Within vitrinites it is possible to distinguish: 

1. 'biochemical gelification' which occurs during the peat and soft brown-coal stages and which is 

governed by the original materials, facies, water and ion supply, degree of alkalinity and the 

oxidative conditions; and 

2. 'geochemical gelification' which affects all the vitrinites in the hard brown coal coalification 

stage. Most geochemical coalification appears to occur close to the boundary between dull brown 

coal and bright brown coal. Geochemical coalification results in the textures that are characteristic 

of coals of bituminous rank.


In Northern Europe, most higher rank coals are from the Carboniferous and most lower rank coals 

from the Tertiary. It can be argued that this lead historically to the differences due to type not 

always being appropriately classified compared with those attributed to rank and that this has lead 

to a much more complex classification than could have been developed. In particular, the continuity 

of the rank changes in vitrinite could have been more properly emphasised over the textural 

differences that result from rank changes. 

This presentation attempts to avoid these additional complexities while including the terms 

appropriate to Tertiary coals. It should be noted that very low rank Permian and Carboniferous coals 

(seen for example in Australia and the mid-west and western plains of the USA respectively) in 

textural terms, resemble higher rank coals of similar age rather than lower rank Tertiary coals. 

Many of the illustrations in this presentation are from low rank Permian and Carboniferous coals 

that are very low in rank (vitrinite reflectance between 0.30% and 0.42%) but the textures of these 

coals are similar to medium rank coals of similar age rather than to Tertiary coals. 

PROPERTIES OF VITRINITE 

Vitrinite has optical properties lying between those of the macerals of the liptinite and inertinite 

groups at low and medium of rank or maturation. At higher levels of organic metamorphism, the 

optical properties of liptinite converge on those of vitrinite so that beyond a reflectance of about 

1.4% distinction of the two groups becomes difficult or impossible. The convergence point varies 

with the age of the rocks so that convergence is delayed until 1.4% vitrinite reflectance for the 

Carboniferous, 1.2% for the Permian, between 1.1% and 1.2% for the Mesozoic and by about 1.0% 

for most of the liptinite within sequences of Tertiary age. 

The reflectances of vitrinite and inertinite also converge at higher levels of organic metamorphism. 

Within the anthracitic range, overlap occurs and the reflectance of much of the inertinite may lie 

between the maximum and minimum values for the vitrinite. 

As well as there being a convergence in optical properties between the maceral groups, a 

convergence occurs at reflectances above about 0.80% of properties within the maceral groups. For 

example, distinction between telovitrinite and detrovitrinite is relatively easy up to a vitrinite 

reflectance of about 0.8% but becomes increasingly difficult above that value. By a reflectance of 

about 1.2% the distinction between telovitrinite and detrovitrinite becomes very difficult, and due to 

the convergence of other properties is generally less important than it is at lower ranks. 

At low ranks, vitrinite shows lower absorption at the blue end of the spectrum resulting in lower 

rank vitrinite having a slight bluish cast. At higher ranks, the dispersion curves become flat and then 

show stronger absorption in the blue resulting in a slight yellowish cast – similar to that shown by 

inertinite but generally less marked. This change in colour cast is extremely important in the 

distinction of vitrinite from inertinite at medium ranks for dispersed organic matter (DOM). 

In terms of chemical composition, vitrinite has a hydrogen content between those of liptinite 

(higher) and inertinite (lower) and it is said to be orthohydrous. For vitrinite at low levels of rank or 

maturation, hydrogen content is typically within the range 5.1 to 5.4% and the H/C atomic ratio is 

between 0.7 and 0.8. Oxygen content is high within low rank vitrinites but decreases rapidly with 

increasing levels of organic maturation. Most of the oxygen is present as functional groups and 

these are eliminated with the generation and expulsion of carbon dioxide and water. 

In vitrinites of maturation similar to those of low rank bituminous coals, about 70% of the carbon is 

bonded in aromatic groupings but about 50% of the hydrogen is present with aliphatic bonds. Most


of the aliphatic hydrogen is present as methyl or methoxy groups but some long chain compounds 

are also present. The aromatic hydrogen occur on the periphery of the aromatic rings. Vitrinite is 

thought to consist of polyaromatic clusters. At low levels of organic metamorphism these are 

relatively small and have a small stacking height. On average, the clusters have their greatest 

dimension in the plane of the bedding, but the structure is turbostratic. In between the aromatic 

clusters, or micelles, other groupings, such as long chain aliphatic compounds are present. With 

increasing levels of metamorphism, the size of the clusters increases, the clusters have a greater 

tendency to become stacked and the degree of preferred orientation. In part, this growth and reorientation 

is made possible by the elimination of the molecules lying in between the micelles. 

Vitrinite within the bituminous rank range becomes plastic on heating and this property enable it to 

form coke structures. At low rank the vitrinite semi-coke appears isotropic but X-ray studies show 

that the structure has become strongly graphitized. With increasing rank, graphitic units within the 

coke become visible with an optical microscope. The size of these mosaic units can be used to 

estimate the rank of the vitrinite prior to coking. These phenomena occur during artificial coking 

and are also seen in natural cokes. Coking occurs under laboratory conditions over the temperature 

range of about 380 o C to 500 o C, may occur under markedly lower temperatures in association with 

contact alteration. Bitumens also develop coke textures, but typically show larger mosaic units 

compared with vitrinite-derived cokes. 

Vitrinite is a major source of catagenic gas at high levels of maturation. At lower levels of 

maturation its role in hydrocarbon generation is uncertain. It is now commonly agreed that vitrinite 

generates some liquid hydrocarbons. 

The extent to which migration from vitrinite can occur remains in dispute. Within the lower and 

middle parts of the bituminous rank range (0.5%


distinction of the edges of individual lenses may be difficult without special techniques such as 

etching. 

Telovitrinite is most prominent in coal seams but it is also found as dispersed organic matter within 

some epiclastic lithologies. Where it occurs with coarse grained epiclastic rocks (typically 

sandstones, but also siltstones and conglomerates), telovitrinite can be allochthonous or 

autochthonous in origin with roots commonly preserved as autochthonous telovitrinite. Where 

telovitrinite is present in fine grained rocks such as claystones, it is commonly autochthonous. The 

extent of compaction of cell structures within telovitrinite provides a measure of physical rank 

change that is to some extent independent of chemical rank change as indicated by vitrinite 

reflectance. In extremely cool deeply buried sections, textures similar to those found in Medium 

Rank D coals can be found with vitrinite reflectance values less than 0.40%. 

Colour and reflectance: 

Most telovitrinite appears grey in polished section. Studies on the dispersion of vitrinite show that 

reflectance is biased towards the blue end of the spectrum at low and medium ranks but dispersion 

curves for telovitrinite undergo a transition to a slight red bias with increasing rank. For this reason, 

in addition to their higher reflectance, high rank telovitrinites appear to have a weak yellow cast to 

the grey. In low rank brown coals, a range of colours occurs. Where cell chemistry has been only 

partially altered, red internal reflections may be visible, but where gelification is more complete, 

telovitrinite appears grey even in very low rank coals. 

A range of colours is not found except in coals of very low rank (less than about 0.35% vitrinite 

reflectance). At all ranks, within isometamorphic coals, a range of reflectance is found. Cell 

structure, where visible, is typically delineated by changes in reflectance. The reflectance of the 

middle lamellae may be higher or lower than that of the remainder of the cells. Telovitrinite 

derived from leaf tissue typically has a lower reflectance than telovitrinite derived from woody 

tissues. Some forms of root tissue also have an unusually low reflectance. 

Within peats and very low rank coals, telovitrinite reflectance is typically lies within the range of 

0.25% to 0.35%. Some peats have telovitrinite reflectances of about 0.3%. Telovitrinite in a few 

low rank coals has a reflectance in the range 0.10 to 0.25% but these low reflectances appear to be 

related to unusual types of plant tissue. 

Reflectances of less than 0.1% are found in structured tissue but these occurrences are probably 

transitional to suberinite, resinite or cutinite. The standard deviation for low rank coals is typically 

about 0.03%. With increasing rank, telovitrinite reflectance increases. It has been a common view 

that vitrinite reflectance is too irregular at low rank for use in determining rank variation. This view 

seems to arise from the presence of marked type-related variations in a small number of coals and 

the low reflectance gradient that typically occurs with depth over the rank range 0.25 to 0.45%. 

Data from deep boreholes show that although reflectance gradient is typically low, the trend for 

increasing reflectance with depth is the dominant feature of the data. 

Telovitrinite reflectance increases with increasing rank and in the lower part of the bituminous rank 

range, the range of reflectance variation is slightly higher than at lower or higher ranks. Where 

telovitrinite reflectance is about 1.0%, the standard deviation for telovitrinite reflectance is typically 

about 0.03 to 0.35% and the range of reflectance in a single coal is about 0.15 to 0.2%. At higher 

ranks, less contrast can be seen between various types of vitrinite, but reflectance variation is still 

present. Where reflectance is measured in non-polarised, or in elliptically polarised light is 

measured (Rm) the range of variation increases due to the effects of increasing bireflectance. 

Dispersion of values for maximum reflectance also increases although to a much lesser extent than


for Rm. Increase in dispersion of maximum reflectance is due, in part, to the difficulties associated 

with finding the exact position of the maximum reflectance and, in part, to the increasing 

significance of strain patterns within vitrinite layers. 

Autofluorescence 

At low rank, autofluorescence is common in telovitrinite. It tends to be preferentially associated 

with the less gelified telovitrinite macerals rather than with ulminite. This primary fluorescence can 

be due to the presence of materials with liptinite affinities (resinite, suberinite or cutinite) of the 

persistence of cellulose into the soft brown coal rank stage. In a small number of vitrinites, primary 

autofluorescence persists into the bituminous rank range where it is always due to the presence of 

materials with liptinite affinities. Most of the telovitrinites showing primary autofluorescence are 

Mesozoic in age. 

Most telovitrinite in hard and bright brown coals lacks autofluorescence. Within the bituminous 

rank range, autofluorescence from telovitrinite becomes a prominent feature. This secondary 

autofluorescence is due to the presence of bitumens rather than primary plant components. There 

are examples where primary fluorescence is present associated with vitrinite up to vitrinite 

reflectances of as high as 0.90%. 

Polishing hardness: 

Telovitrinite shows lower polishing hardness compared with both inertinite and liptinite. It also 

shows a lower polishing hardness compared with most detrovitrinite. Within individual lenses of 

telovitrinite, some polishing relief is commonly present. 

Common associations: 

Telovitrinite forms the major part of the bright bands in hard coals. It is also a major component of 

most other coal lithologies. In some coals, an association between telovitrinite and structured 

inertinite (fusinite and semifusinite) can be demonstrated. Due to the greater frequency of fractures 

within telovitrinite compared with other macerals, there is also an association between telovitrinite 

and exsudatinite. There are also associations between telovitrinite and some forms of occurrence of 

resinite (with both wood-related and leaf-related resinites), cutinite and suberinite. The large 

woody masses found in some types of brown coal are dominantly preserved as telovitrinite. 

Origin: 

Where plant tissue becomes humified but retains a more or less intact cell structure, it is normally 

preserved as telovitrinite. Both woody and leaf tissues can be preserved as telovitrinite. Cell 

preservation ranges from the primary cell wall only to preservation of secondary cell walls. In 

some examples, internal structures within the secondary cell walls can be resolved. 

Distinction from other macerals: 

The moderate to large size and intermediate reflectance of telovitrinite are the primary 

distinguishing features. Heterogeneity is typically limited to the presence of plant cell structure 

although in some occurrences inclusions of resinite or of suberinite are present. 

Telovitrinite is distinguished from semifusinite on the basis of lower reflectance and less distinct 

cell structure. Semifusinite at any given level of coal rank, tends to have a more open cell texture


but the presence of open cell texture cannot be used as a distinguishing feature from semifusinite 

where the mean vitrinite reflectance is less than about 0.5%. 

Massive telovitrinite and gelovitrinite are similar. Gelovitrinite is rare and typically occurs in cross 

cutting veins. Telovitrinite is typically sub-parallel with bedding and may contain genetically 

associated inclusions of macerals such as resinite or suberinite. 

Telovitrinite is distinguished from detrovitrinite by the absence from telovitrinite of macerals such 

as sporinite and inertodetrinite. Detrovitrinite may show small domains about the size of plant cells 

but other attrital macerals are normally present. At ranks in the range 1.0 to 2.0%, where liptinite 

reflectances have converged on those of vitrinite, the distinction of telovitrinite from detrovitrinite 

may become difficult or impossible. At higher ranks, the use of crossed polars normally permits the 

distinction of these maceral subgroups. 

PROPERTIES 

Telovitrinite typically has a higher reflectance and lower hydrogen content than detrovitrinite. Most 

of chemical analyses in the literature relate to telovitrinite because of the greater ease of separating 

telovitrinite from other maceral. Cleat fractures are best developed within telovitrinite and are more 

prominent in higher rank coals. Cleats tend to be more open in the thicker layers of telovitrinite and 

more frequent in thinner layers of telovitrinite. 

Macerals within the telovitrinite subgroup 

The main variations within telovitrinite relate to the degree of gelification. Gelification can occur 

as a result of processes within the peat stage and is a normal response to physicochemical 

coalification. Telovitrinite is divided into: 

Textinite - well preserved and intact cell walls and cell lumens that are largely open. 

{Texto-ulminite - intermediate in texture between textinite and ulminite, cell lumens are partly 

open but infillings of cells with gelified material and collapsed cell walls are much more 

common than for textinite. Useful term but no longer in use} 

Ulminite - telovitrinite having a structure that is substantially massive but the layers may show 

small voids that are typically related to original cell structures. 

Collotelinite - layers and lenses that typically lack cellular structure when viewed in oil immersion 

but are derived from stems, roots bark and leaves that retain cell structures. 

Textinite is present in coals that have undergone minor amounts of burial - of the order of 300 to 

600 m maximum cover. Texto-ulminite – material transitional between textinite and ulminite - is 

present in peats and persists down to about 1500 m of cover but the proportion of open cell lumens 

decreases markedly where the cover exceeds about 900 m. Where cover has been greater than 

about 1500 m, telovitrinite is present as collotelinite. 

2.3.3.1.2 DETROVITRINITE SUBGROUP 

Shape and size: 

Detrovitrinite consists of phytoclasts that are derived from fragments of plant tissues together with 

material that has been precipitated from colloidal solution. Cell wall and cell contents material may 

both be present. They do not retain their original botanical relationships but some or the original 

plant structures at the cell level may be distinguished. The colloidal material is similar in optical 

properties and chemical composition to the discrete plant fragments present in detrovitrinite.


Detrovitrinite occurs as groundmass material and commonly contains inclusions of macerals of the 

inertinite and liptinite groups. Textural features within detrovitrinite can be distinguished in low 

rank coals, especially brown coals. In coals of bituminous rank detrovitrinite becomes 

progressively more homogeneous optically and the main textures in detrovitrinite of higher rank 

coals are associated with inclusions of other maceral groups and mineral matter. Within higher rank 

bituminous coals (vitrinite reflectance greater than about 1.4% for coals of Carboniferous age, 

1.25% for Permian coals, about 1.2% for Mesozoic coals and about 1.15% for most coals of 

Tertiary age), liptinite inclusions cannot be distinguished from the detrovitrinite groundmass. 

Within the anthracite rank range the distinction of inertinite from detrovitrinite becomes difficult 

unless polarised light is used. Inertinite is more readily distinguished from detrovitrinite in 

anthracites if the block is rotated to the minimum reflectance position or the field is viewed in 

partially crossed polars. 

In addition to the inclusions of other macerals that are visible using an optical microscope, studies 

using transmission electron microscopy has shown the presence of small inclusions of liptinitic 

material. Some of these represent material similar to macerals that can be resolved optically within 

the liptinite group. Other inclusions may represent different types of entities such as the coatings of 

bacterial cells. Detrovitrinite also probably contains inclusions of dispersed lipid related molecules. 

Such dispersed lipid related material may be present in both the fragments of plants cells and in the 

material precipitated from colloidal solution. 

Compaction structures can commonly be seen around inclusions of other macerals because 

detrovitrinite compacts during coalification to a greater extent than macerals of the liptinite and 

inertinite groups. Vitrinite exhibits plastic (rheid) behaviour during coalification and this is most 

noticeable within layers of detrovitrinite. 

Mineral inclusions are common within detrovitrinite. Much of the syngenetic adventitious mineral 

matter in coal seams is associated with detrovitrinite. The mineral matter occurs as small grains, 

but these may be sufficiently abundant to form lenses dominated by mineral matter. 

Detrovitrinite occurs within coal seams. In Palaeozoic coals, it is most abundant in semi-bright 

lithologies (clarain and duroclarain). Most coals of Tertiary age are dominated by vitrinite group 

macerals and it is difficult to relate the abundance of detrovitrinite to the brightness of the coal. The 

most abundant forms of vitrinite found as dispersed organic matter within sediments are referable to 

detrovitrinite. Detrovitrinite within sediments other than coal ranges from strong positive polishing 

relief to weak negative relief relative to the adjacent mineral matter. Forms with positive polishing 

relief are more common than those with low or negative relief. Where reworking has been 

prominent, virtually all vitrinite phytoclasts have positive polishing relief. 

Detrovitrinite occurring within epiclastic rocks and carbonates is allochthonous. Within coals, 

detrovitrinite ranges from hypautochthonous to allochthonous. Hypautochthonous detrovitrinite is, 

however, probably more common than allochthonous detrovitrinite. 

Polishing relief for detrovitrinite is an important feature. Higher polishing relief occurs in 

phytoclasts transitional to inertinite and those containing liptinite inclusions such as suberinite. 

Colour and reflectance: 

Detrovitrinite appears grey in polished section. In coals of medium rank it typically has a lower 

reflectance than that of the telovitrinite. However, this is not always the case. The causes for this 

difference include the presence of low reflecting tissues preserved as telovitrinite and the presence


of high reflecting attrital fragments within the detrovitrinite related to corpocollinite. At higher 

ranks, distinction of detrovitrinite from telovitrinite maybe difficult or impossible in plane polarised 

light. The use of partially crossed polars may permit their distinction on the basis of slight 

differences in bireflectance and the greater ease of detection of inclusions of liptinite and inertinite 

within the layers of detrovitrinite. A quarter wave, or a one wave plate inserted in the light path 

may also assist in distinguishing these maceral sub-groups at higher rank. In thermally altered 

coals, bireflectance tends to be low and the distinction of these sub-groups is especially difficult for 

this category of coals. 

The distinction of detrovitrinite from telovitrinite becomes progressively more difficult with 

increasing rank. By about a vitrinite reflectance of 0.80% in most cases the fragmental nature of 

detrovitrinite is more inferred than directly observed and by about a vitrinite reflectance of 1.20% 

textural differences between the sub-groups are more or less absent. 

Autofluorescence 

At low ranks, autofluorescence is rare in detrovitrinite. At medium ranks, detrovitrinite may show 

moderate to strong fluorescence associated with the presence of bitumens. Above 1.0% vitrinite 

reflectance, fluorescence of vitrinite may be stronger than for associated liptinite macerals. 

Polishing hardness 

The polishing hardness of detrovitrinite is commonly greater than that of telovitrinite but less than 

that of all of the liptinite and inertinite macerals. 

Common associations 

Detrovitrinite forms the mesostasis of most semi-bright coal lithotype. It is commonly associated 

with sporinite, resinite, liptodetrinite, suberinite, inertodetrinite and semifusinite. In Tertiary coals, 

it is commonly associated with sclerotinite. 

Origin 

Detrovitrinite is formed from degraded plant material within peat swamps. Degraded vitrinite precursors 

become mixed with other maceral pre-cursors to form a mesostasis of detrovitrinite with 

inclusions of the other macerals. During coalification, gelification increases and compact textures 

typically develop within the detrovitrinite while immature textures are still present within the 

telovitrinite. 

Inclusions of other macerals are present at a microscopic scale and electron microscope studies have 

shown that liptinitic inclusions are also present at a sub-microscopic scale. Some of these probably 

represent small fragments of liptinite macerals but some probably have an origin from bacterial and 

fungal lipids. However, such lipids are presumably present within telovitrinite as these tissues have 

also been subject to bacterial and fungal degradation. The extent of degradation is more extreme 

for detrovitrinite and, in many cases, it represents as residue resulting from intense biochemical 

degradation. Thus, detrovitrinite is a biological remanié deposit. 

Distinction from other macerals 

At low and medium ranks, detrovitrinite has a higher reflectance than liptinite and a lower 

reflectance than inertinite. Compared with telovitrinite, detrovitrinite lacks continuous cell 

structures and contains a wider range of inclusions of other macerals. Compared with inertinite,


detrovitrinite at low to medium levels of maturation appears slightly blue grey but the colour 

approaches that of low reflecting inertinite at about 1.20% and distinction from inertinite becomes 

more difficult in the range vitrinite reflectance from about 1.20% to 2.0% where vitrinite develops 

distinct bireflectance. 

Bituminite and detrovitrinite share some characteristics and where only one of these macerals is 

present, it may be difficult to distinguish bituminite from detrovitrinite. Bituminite has a much 

lower reflectance and typically contains more abundant inclusions of micrinite and liptinite. In 

some coals, degraded cork tissue with high reflecting and weakly to non-fluorescing suberinite can 

show gradations into detrovitrinite. If cell wall structures can be distinguished, the material is 

referred to suberinite. 

PROPERTIES 

Detrovitrinite commonly shows a lower reflectance than telovitrinite. In some coals, particularly 

those where corpogelinite is abundant, the reflectance of detrovitrinite may be higher than that of 

telovitrinite. Low reflecting detrovitrinite is perhydrous and some examples have a hydrogen 

content of about 6%. 

Macerals within the detrovitrinite subgroup 

Attrinite - fragmental cell wall and cell contents with poor preservation and discrete boundaries 

between most of the constituent grains. Attrinite is the characteristic mode of occurrence for 

detrovitrinite in soft brown coals and its presence indicates burial depths of less than about 

500 m. 

Densinite- intermediate in texture between attrinite and vitrodetrinite and collodetrinite, densinite 

has a granular texture but most of the grains are cemented to the adjacent grains and few voids 

are present. Densinite forms when the grains within attrinite become cemented by colloidal 

humic material but the sutures are still visible in most cases. 

Vitrodetrinite – consists of small particles of vitrinite but the boundaries between particles become 

obscured with increasing rank. 

Collodetrinite - detrovitrinite having a structure that is substantially massive. It forms when the 

grains in densinite become so fused (gelified) that the boundaries can no longer be 

distinguished. 

2.3.3.1.3 GELOVITRINITE SUBGROUP 

Gelovitrinite forms a third subgroup of macerals. Material referred to gelovitrinite is presumed to 

have passed through a structureless colloidal stage during the biochemical coalification. It is 

seldom possible to demonstrate this for any given entity without special treatments such as etching 

the surface of the sample with a powerful oxidized agent. Where such gelified tissue is included 

within telovitrinite, it is common practice to include it with the telovitrinite. Thus, most 

corpogelinite and porigelinite would be included within telovitrinite. Eugelinite is extremely rare if 

these restrictions are used. Within some coals, there are highly distinctive veins of gelinite and so 

the term is retained. In general, it is preferable to restrict assigning material to the gelovitrinite 

subgroup. If there are alternatives within telovitrinite and detrovitrinite, their use is usually 

preferable. 

In most coals, gelovitrinite is a minor component of the total vitrinite. 

Macerals within the gelovitrinite subgroup


Corpohuminite – structureless bodies filling cell lumens. In some usages this term includes 

phlobaphinite. 

Corpogelinite – structureless bodies derived from humic cell filling, may occur isolated from the 

source tissues or in situ. 

Gelinite- a maceral of secondary origin and can occur as cell filling or more rarely as discrete veins. 

2.3.3.2 THE LIPTINITE GROUP 

In coals of low and medium rank, liptinite macerals have a reflectance much lower than that of 

vitrinite and typically show autofluorescence when illuminated with ultra-violet, violet or blue light. 

With increasing rank, liptinite reflectance increases. This increase at first lags behind the rate of 

increase in vitrinite reflectance but in the medium volatile bituminous rank range, liptinite 

reflectance converges rapidly with that of vitrinite. Liptinite fluorescence decreases in intensity 

with increasing rank and shows a shift to the red part of the spectrum. At, or before, the 

convergence of reflectance with that of vitrinite, fluorescence becomes extinct with normal 

excitation methods. Within some samples at higher ranks, liptinite maximum reflectance can be 

seen to be greater than that of vitrinite and in these samples the two maceral groups can be 

distinguished. Commonly, however, because of the convergence of reflectance and the loss of 

fluorescence from liptinite, they cannot be distinguished in coals of higher rank. 

Most of the macerals within the liptinite groups are derived from specific tissue types, the exception 

being liptodetrinite, where the origin is uncertain because of small size of the phyterals. 

Distinguishing features of liptinite 

Liptinite is distinguished initially from other macerals on the basis of its lower reflectance. 

Following the establishment of fluorescence-mode observations as a routine technique, 

autofluorescence properties have become an important secondary distinguishing feature. 

Most of the liptinite macerals have an origin from distinct types of plant tissue and morphology is a 

further important distinguishing feature. Where liptinite morphology is present but the optical 

properties are those of inertinite (most commonly the case for fusinized resin but also reported for 

megaspores), the phyteral is referred to the inertinite group. Thus, although the morphology of 

liptinite group macerals is distinctive, its use in classification is secondary to reflectance at the 

maceral group level. Within the liptinite group, morphology is the main criterion used to assign 

liptinite to specific macerals. 

PROPERTIES 

Liptinite macerals have a low reflectance and a high hydrogen content until their properties 

converge with those of vitrinite. During carbonization, they have a high make of liquids and gas. 

Although they are rich in hydrogen, with H/C atomic ratios commonly in excess of 1.0, many 

liptinite macerals probably do not contribute greatly to the generation of liquid hydrocarbons. This 

is because many of the macerals have a structure that is based on naphthenic units rather than 

paraffinic units. Most primary oils are paraffinic in character and the naphthenic components do 

not appear to contribute to the bulk of liquids generated. The chemical affinities of the liptinite 

group of macerals are shown in Table 2.3. 

Contributions to the generation of liquid hydrocarbons under conditions of normal maturation are 

probably restricted to the macerals in the second and third columns of Table 2.2. For this reason, a 

detailed knowledge of the macerals present within the liptinite group is required for an assessment


of hydrocarbon generation potential (and of the maturation windows within which generation takes 

place). Liptinite group abundance or the presence of high hydrogen contents in bulk analyses (for 

example Rock-Eval HI) are not an unequivocal indication of source potential. Some terrestrial 

facies are dominated by sporinite or resinite and have low oil source potential. Other coal-related 

facies have a high content of cutinite or of suberinite and have a much higher source potential. 

Most liptinite-rich lacustrine facies are dominated by alginite and usually have high source 

potential. Marine liptinite is dominantly lamalginite or bituminite and both of the macerals have a 

high source potential for petroleum liquids. Liptinite type and abundance is an important element 

of organic facies. A classification of liptinite-rich rock types has been proposed by Cook and 

Sherwood (1991) to assist in defining organic facies and petroleum source potential. 

Telalginite has the highest hydrogen content of all the liptinite macerals and gives the highest 

liquids yield when artificially heated in a retort. However, under natural conditions, there is 

evidence that the carbon-carbon bonds in the paraffinic structures are strong enough to resist 

breakdown until temperatures are reached where the structures tend to aromatise. Thus, under 

natural conditions, the liquids yield from telalginite may be lower than from macerals such as 

lamalginite that have a lower hydrogen content but contain more labile chemical structures and gas 

yields may be correspondingly higher. 

2.4.1 SPORINITE 

Sporinite is the term given to spore and pollen coats. These are composed of material generically 

termed sporopollenin. This has a dominantly naphthenic structure. Morphologically, the material 

preserved most commonly is the spore or pollen exines and more rarely the entine may be 

preserved. The dominance of spore exines in most Palaeozoic coals gave rise to the term EXINITE 

for the group of macerals now termed liptinite. 

Sporinite varies in the nature of its preservation but it commonly retains its ornament and shows 

relatively little change, apart from becoming flattened until the bituminous rank range. Within this 

rank range marked changes occur due to coalification. 

TABLE 2.7. CHEMICAL AFFINITIES OF THE LIPTINITE MACERALS. 

NAPHTHENIC PARAFFINIC AROMATIC 

SPORINITE CUTINITE 

RESINITE SUBERINITE 

LIPTODETRINITE ALGINITE BITUMINITE (but includes a large 

amount of aliphatic material, 

probably derived from bacterial 

lipids 

SECONDARY MACERALS AND BITUMENS 

EXSUDATINITE BITUMENS SUCH AS 

OZOCERITE 

IMPSONITES AND EPI- 

IMPSONITES, BITUMEN 

COKES


In Palaeozoic coals, megaspores (female) are commonly present. These are up to about 2 mm in 

diameter and typically show weaker fluorescence than microspores (male). However, it is usually 

not possible to determine the gender of the smaller spores so they are normally termed miospores. 

In Tertiary coals sporinite occurs with detrovitrinite but is commonly only a minor constituent. The 

fluorescence intensity of most sporinite is relatively low even in low rank Tertiary coals and it 

shows a pronounced spectral bias towards orange or dull orange. Sporinite is not common in dom 

in Tertiary sequences except within a restricted number of canneloid claystones. In this association, 

fluorescence intensity tends to be much greater compared with sporinite in Tertiary coals. 

2.4.2 CUTINITE 

Cutinite represents the outer coating of leaves, needles, shoots and some roots and thin stems. In 

leaves, it has a distinctive cellular pattern in plan view and in section has projections where the 

cuticles extend down at the side of the palisade cells. The projections give cutinite a very 

characteristic serrated appearance in cross section. Cutinite ranges in thickness from about 0.003 

mm to about 0.02 mm. Typically, thin cutinite shows fluorescence that is less intense than that 

from thick cutinite. In general, cutinite thickness is determined by the floral assemblage and that as 

might be expected, dry climate floras generally tend to have thicker cutinite 

Cutinite has long chain structures that are waxy in nature. It is probable that during coalification, 

waxy alkanes can be generated from cutinite. However, a condensed, aromatic residue is left within 

the coal. 

Cutinite is present in most coals and is the dominant liptinite maceral in some Mesozoic coals and 

less commonly in Tertiary coals. In Tertiary coals, leaf tissue preserved as vitrinite may be 

common without cutinite being abundant. Where vitrinite reflectance is relatively high (above 

about 0.9% for Mesozoic coals and above about 0.6% to 0.7% for Tertiary coals), the cutinite may 

be essentially non-fluorescing. Up to reflectances of about 1.2% it may still be possible to identify 

cutinite in reflected white light mode. With very high rank coals, distinction of cutinite from 

vitrinite may be possible on the basis of cutinite having a higher bireflectance. 

In Tertiary coals, the dominance of tenuicutinite and the absence of strong fluorescence from most 

of the cutinite presumably relates to the lack of a need for thick cuticular tissue with a high cutin 

content to prevent desiccation. Some thick walled and more brightly fluorescing cutinite is present 

in Tertiary coals. Tissue with multiple cuticles is found in some coals and the tissue structures may 

be transitional to suberinite. Cutinite from the Paleozoic commonly retains distinct fluorescence up 

to vitrinite reflectances in the range 1.1 to 1.3%. In some Tertiary sequences, the cutinite is largely 

non-fluorescing in association with vitrinite reflectances of about 0.8%. These differences could 

relate to the rates at which coalification occur but seem more likely to be due to compositional 

changes with time in cutan, and hence cutinite, as a result of evolution within plants. 

The Triassic is commonly associated with the presence of thick cutinites, usually with strong 

fluorescence. In part, these differences are due to floral changes but climate is probably an 

additional factor. 

Detrital cutinite is present in many rocks, including some that are fully marine, but it appears that 

cutinite degrades much more rapidly during transport compared with sporinite. 

2.4.3 SUBERINITE


Suberinite is derived from the outer layers of woody tissue. The cell walls are impregnated with 

suberins. These are compounds with affinities to n-alkanes. Suberinized tissues have a similar 

function to cuticles, but being much thicker, may prevent plants from physical damage as well as 

protecting them from desiccation. Typically suberinite has a blocky appearance and the cells are 

filled phlobaphenes preserved as the maceral phlobaphinite (included in this study within 

telovitrinite or detrovitrinite depending on the extent of tissue preservation). 

Suberinite is present in most Mesozoic and Tertiary coals but is rare in most Palaeozoic coals. It is 

the dominant liptinite maceral in some Mesozoic and Tertiary coals. The most widely distributed 

form of suberinite in Tertiary coals is thin walled and weakly- to non-fluorescing. If this form is 

present with well-preserved cell contents , such as the associated woody tissue or the cell lumens 

within the suberinite, suberinite seldom forms a major component of the coal. Where the other cell 

tissues have been degraded by bacterial or fungal activity, suberinite is concentrated as part of a 

remainé effect and in these cases forms a major proportion of some layers. 

A second form of suberinite occurs as much thicker and more brightly fluorescing tissues that are 

commonly relatively well preserved, thick and laterally extensive. Typically this thicker form of 

suberinite is most commonly seen in the Miocene and is especially abundant within coals formed in 

ombrogenous mires but possibly related forms have been observed within some Eocene coals. For 

this form, strong fluorescence intensity is retained up to about 0.65%, and together with resinite, it 

is commonly the most strongly fluorescing component in Tertiary coals of bituminous rank. Some 

of the thick walled suberinites from the Tertiary are the last of the liptinite macerals to show a 

convergence of reflectance with that of vitrinite and may show distinct fluorescence up to a vitrinite 

reflectance of about 1.15% whereas most of the other liptinite macerals in Tertiary coals show weak 

or no fluorescence beyond about 0.90%. 

A working group on suberinite has been established as it appears that outside the coals that have 

been studied most intensively (the Carboniferous and the Permian) suberinite and related entities 

are not always well understood. Within a few coals of Jurassic age, suberinite can be not only the 

most abundant liptinite maceral, but the most abundant maceral within the whole coal. Associations 

of suberinite, resinite and cutinite derived from various floras can present aspects that differ from 

those figured in the original descriptions of suberinite. 

Suberinite is difficult to distinguish as a separate component in non-coaly rocks unless it is 

unusually abundant. It is however commonly present in phytoclasts preserved as telovitrinite and 

detrovitrinite. Care is needed to avoid measuring suberinite within small vitrinite phytoclasts 

especially as it may show very weak fluorescence. 

2.4.4 RESINITE 

Plants commonly impregnate tissues with naphthenic compounds to deter attack by insects, fungi 

and bacteria and some similar compounds are a byproduct of metabolism of plants. Wood, 

periderm and leaf tissues may all contain resin bodies. Additionally, resin secretions develop on 

tree trunks and at the base of trees where the wood has become damaged, typically due to insect 

attack. 

Resinite is rich in hydrogen but is dominated by complex naphthenic compounds. Some of the 

Paleozoic resins seem to have been susceptible to oxidative polymerization and are preserved as 

inertinite. This does not appear to be a feature of resins of Tertiary origin. 

Resin bodies may contain some internal structures where more than one phase is present. The 

outside of the lenses is commonly smooth but may be scalloped. Both the internal structures and


the external shape have caused incorrect assignment of resinite to alginite by some previous 

workers. The internal structures can be similar to those in bitumen. Resinite can become mobilized 

and transitions to exsudatinite occur. 

In Tertiary coals, resinite is typically the dominant liptinite maceral in samples where liptinite is 

unusually abundant. Resinite occurs in a number of associations. Resinite may be associated with 

leaf tissue or with woody tissue and in these associations occurs within telovitrinite. Wood 

associated resinite occurs as moderate to large lenses whereas leaf-resins occurs as numerous but 

smaller bodies. A third mode of occurrence is within attrital layers containing detrovitrinite and 

other liptinite macerals, especially liptodetrinite. Resinite occurring in this mode appears to be 

concentrated as a result of the degradation of resin bearing tissues. The abundance of resinite in this 

mode of occurrence is a remainé effect. More rarely these detrovitrinite associated resinite rich 

layers may be of detrital origin. 

Most resinite in Tertiary coals shows very strong fluorescence and in some coals much could be 

referred to the term fluorinite. Fluorinite has not been distinguished here from resinite because of 

the lack of a clear distinction for these macerals. Most resinite bodies lack oil cuts when 

illuminated with UV/violet light for fluorescence observations but a proportion emits streaming 

greenish yellow oil cut.). 

Resinite is commonly associated with exsudatinite, especially in some sections of Tertiary coal 

measures. In places, the exsudatinite veins are sufficiently thick to permit collection of hand 

specimens at the kilogram level. The composition of this form of exsudatinite appears to be very 

similar to that of associated resinite. Detrital resinite is common in many sections, but generally 

occurs close to deltaic facies. 

2.4.5 LIPTODETRINITE 

Liptodetrinite represents mechanically or biochemically degraded liptinite that has no recognisable 

form. Where form is retained, the material is referred to the appropriate maceral. It may be 

possible to infer affinities of liptodetrinite from its associations, but no subdivisions are made to 

recognise possible affinities. 

Liptodetrinite is very widely distributed within coals. It is preferentially associated with attrital 

layers where it occurs with detrovitrinite, resinite and sporinite. From the association, in Tertiary 

coals, with resinite, it seems probable that a high proportion of this liptodetrinite represents small, 

or fragmented, resin bodies. In canneloid coals, some of the liptodetrinite may have an affinity with 

sporinite and it is possible that some is related to degraded suberinitic tissue. Some lithologies with 

abundant liptodetrinite of probable algal affinities are also known. 

Liptodetrinite is also widely distributed within sedimentary rocks other than coal. 

2.4.6 ALGINITE 

Alginite has been divided on the basis of morphology into telalginite and lamalginite. 

Telalginite occurs as larger bodies, commonly showing botanical structure and typically with more 

intense fluorescence than most other macerals except some of the more strongly fluorescing resinite 

occurrences. Both marine algae (tasmanitids and Gloeocapsomorpha) and non-marine algae 

(Botryococcus and related forms) can occur as telalginite. Telalginite within coals is typically 

derived from Botryococcus but some shaly coals with tasmanitids are known.


Lamalginite is derived from smaller algae and less commonly shows botanical structure. In 

sections parallel with bedding, botanical structure is relatively commonly preserved. In sections 

perpendicular to bedding, lamalginite has a lamellar form, hence the name. The fluorescence 

intensity of lamalginite is commonly less intense than that of telalginite and it shows less bias 

towards green and yellow. Lamalginite is derived from green algae and can be present in marine 

and in non-marine rocks. 

In marine rocks, the most common sources are acritarchs and dinoflagellates, but other algae 

probably contribute to lamalginite. In lacustrine rocks, green algae such as Pediastrum are the 

major forms contributing to lamalginite but a number of other genera may also be present. In both 

marine and non-marine assemblages of lamalginite, some brightly fluorescing entities may be 

present. 

Lamalginite and telalginite may occur together in both marine and non-marine rocks. Both may 

also occur in coals. Within coals, telalginite is easily distinguished but lamalginite may be difficult 

to distinguish from sporinite. 

Both telalginite and lamalginite have a high content of hydrogen and are dominated by aliphatic 

compounds with affinities to n-alkanes or some types of branched alkanes. Pyrolysis yields from 

alginite are high to very high. Evidence suggests that during normal conditions of maturation or 

coalification, lesser amounts of fluids are yielded compared with pyrolysis. Telalginite, in 

particular leaves an aromatised residue. For lamalginite, the results of maturation are less clear, 

possibly because it is more difficult to distinguish highly coalified lamalginite from other macerals. 

In Tertiary coals, telalginite shows two main types of associations. Firstly, it occurs in coals that 

appear in other respects to be normal humic coals, and secondly with canneloid coals or canneloid 

shaly coals. The colonies show a similar range of size, morphology and preservation in these 

different modes of occurrence. Typically, Tertiary occurrences of telalginite derived from 

Botryococcus, show poor preservation of the morphology in the colonies compared with the 

telalginite from the classic boghead coals of the Carboniferous and Permian. In many Tertiary 

coals, the modal colony size is small, perhaps indicating that conditions were only marginally 

suitable for the growth of Botryococcus. 

Lamalginite is found in sections dating back to the Precambrian. Precambrian lamalginite appears to 

be the major source of the Precambrian oils found in countries such as Russia and Oman. 

2.4.7 BITUMINITE 

Bituminite occurs as layers and lenses in some marine rocks and low reflecting material in 

sapropelic coals (cannels and the bogheads or torbanites) has been referred to as bituminite. The 

origin in marine rocks is thought to be from cyanobacteria with possible contributions from brown 

and red-green algae. A cynobacterial origin for the material in coal is also possible but most of the 

material in the sapropelic coals is probably higher plant in origin. 

Bituminite has optical properties intermediate between those of the classic group of liptinite 

macerals and those of vitrinite. Thus, bituminite is more highly reflecting than other liptinite 

macerals with the exception of some occurrences of suberinite and has a markedly lower reflectance 

than detrovitrinite. In thin section, bituminite is red (vitrinite is also red in thin section), whereas 

other liptinite macerals are yellow. Bituminite typically has very weak fluorescence, exceptions 

apparently relating to impregnation with bitumens. A major distinguishing feature is the abundance 

of micrinite within bituminite.


In Tertiary coals with canneloid affinities, so-called bituminite occurs associated with a wide range 

of other liptinite macerals and is typically interbedded with vitrinite-rich layers. It may well 

represent suberinite in which cell structures are unusually difficult to distinguish. Vestigial cell 

structures may be present in some fields of view and where they are present reference to other 

macerals such as suberinite may be more appropriate. Bitumen impregnation of some of these coals 

results in better resolution of botanical structure. In these cases, it is commonly possible to 

distinguish a range of other liptinite macerals. 

Bituminite within marine rocks appears to be relatively well-defined. Low reflecting weakly 

fluorescing components are present in coals, but the classification of this material appears to be less 

well understood compared with bituminite in marine rocks. Additionally, the origin of the low 

reflecting components within coals is almost certainly different to the bituminite in marine rocks. 

For these reasons a case can be made for restricting the term bituminite to rocks of marine origin. It 

is hoped that some of the current working groups within ICCP will develop a suitable terminology 

for materials within coal that have previously been referred to as bituminite. 

2.4.8 EXSUDATINITE 

Veins of bitumen-like material within coals have been referred to the maceral exsudatinite. The 

maceral name alluded to an assumed origin as an exudate from coal - the author mistakenly thought 

that the English spelled "exude" as "exsude". Similar material had earlier been described as 

secondary resinite. Some occurrence show clear relationships to resinite but many do not. Whereas 

oil cut and oil haze are unusual for resinite, these features are commonly present in association with 

exsudatinite. 

In normally coalified samples, exsudatinite is present as veins of weakly reflecting but moderately 

to strongly fluorescing material. The more strongly fluorescing veins are the most likely to show 

oil cut and oil haze. The presence of more than one generation of veins is a common feature. In 

thermally altered coals, meta-exsudatinite veins may be present. Meta-exsudatinite has a 

reflectance similar to that of the associated vitrinite and does not show fluorescence. In form it is 

similar to exsudatinite. 

Exsudatinite typically occurs as veins. These range up to 3 cm in thickness and in some of the coal 

mine exposures the veins can be followed laterally for some metres. They occupy one of the cleat 

fracture sets but rarely occur in more than one of the cleat sets perpendicular to bedding. They 

commonly have a "V" shaped section providing evidence of having been forcefully emplaced. En 

echelon offsets are common at both the field scale and the microscopic scale. Material similar to 

exsudatinite may also occur in less well-defined masses and these have been referred here to 

bitumen. (In this usage the older geological meaning for the term bitumen is adopted rather than the 

geochemical term for rock extracts. Exsudatinite shows similarities in its mode of occurrence to 

well known bitumens such as the gilsonite veins of the Green River Formation.) However, 

exsudatinite and gilsonite do not appear to be related chemically. 

Some exsudatinite, especially in coals with vitrinite reflectances in the range 0.45 to 0.55%, occurs 

fringing resin bodies. Veins of exsudatinite around the rims of resin bodies show fluorescence 

colours and intensity similar to the resinite. Some coals with a high content of exsudatinite, do not 

have high resinite content, and it is probable that some exsudatinite has an origin independent of 

resinite. Exsudatinite shows an association with telovitrinite. This association may be due, in part, 

to the source of the exsudatinite. However, telovitrinite shows a much higher frequency of cleat 

fractures and this, in itself, would cause an association.


Exsudatinite is especially common in Tertiary coals from Indonesia. It is also common in those 

from Malaysia and Thailand but, for example, is not especially common in those from Gippsland 

Basin. The control over the abundance of exsudatinite may relate to the thermal and uplift history 

of the coals. Where exsudatinite has been analysed it has proved to be naphthenic in composition. 

As sample of exsudatinite from Bukit Asam, near an igneous plug, contained small amounts of 1dienes 

that may have indicated a pyrolytic origin (Gilbert, pers comm.). 

The greatest abundance of exsudatinite noted to date occurs in some of the Miocene coals 

associated with uplift along the folded belt near Samarinda in Kalimantan. Abundance of 

exsudatinite may relate to the rate at which mobile hydrocarbons are produced but rapid uplift and 

freezing of the hydrocarbons within vein structures may be an important control over abundance. 

Exsudatinite is not seen in coals of very low rank and this accords with an origin during maturation. 

Where vitrinite reflectances exceed about 0.8% it is also rare or absent. This suggests that 

exsudatinite is lost as a normal part of the maturation process at higher ranks. 

Meta-exsudatinite is rare, and in the author’s experience is restricted to coals that have suffered 

contact metamorphism. Meta-exsudatinite shows reflectances in the range 1.0% to in excess of 3%, 

depending on the rank of associated vitrinite. 

2.3.3.3 THE INERTINITE GROUP 

2.3.3.3.1 GENERAL 

The inertinite group of macerals are important components of many pre-Tertiary coals but are 

present only as a minor component in most Tertiary coals. Inertinite has a mixed range of origins 

but all the macerals have reflectances higher than that of vitrinite in low and medium rank coals. 

Most inertinite is derived from tissues similar to those that give rise to vitrinite but represent 

preservation under different conditions. Most have a common property of containing oxygen in 

much more stable groupings than is typical of vitrinite. 

Sclerotinite is the most widely distributed inertinite maceral in most Tertiary coals but the average 

percentage of sclerotinite may be less than that of semifusinite or inertodetrinite. Tertiary coals are 

characterized by a paucity of inertinite, the near ubiquitous presence of sclerotinite of fungal origin 

and a dominance of very low reflecting semifusinite where that maceral is present. Even where 

inertinite is present in more than trace amounts, the composition and reflectance of the inertinite in 

coals of Tertiary age is different from the inertinite found in older coals. 

The difference in the inertinite populations between Tertiary and older coals indicates that some 

important factors were different during the peat stage. Tertiary coals have a petrology similar to 

that of Recent peats. Thus, it can be presumed that while present day peats form good analogues for 

Tertiary coals, they are not good analogues in at least some respects for the pre-Tertiary coals. In 

addition to containing larger populations of inertinite, pre-Tertiary coals lack the fungal sclerotinite 

found in the younger coals. The cause for this difference is not clear. A small number of Tertiary 

coals contains both large and diverse populations of inertinite and fungal sclerotinite so the two 

components are not mutually exclusive. Coals with abundant inertinite and fungal sclerotinite form 

only a small proportion of Tertiary coals some of the most notable examples being from Asam in 

northern India, from Venezuela and from Gippsland Basin in Australia. 

PROPERTIES 

Inertinite has a higher reflectance than vitrinite over most of the range of rank or maturation. This 

is partly a function of a higher refractive index but is due in large part to a much higher absorptive


index. In turn this appears to be related to a higher proportion of oxygen occurring in groupings 

that are more stable than the groupings within vitrinite. The origin of the term inertinite relates to a 

less reactive behaviour during coking, although the lower reflecting inertinite can form vesicles and 

a mosaic structure. It is, however, a misnomer in relation to the behaviour of the inertinite group in 

a range of situations. 

The most obvious reactive behaviour of inertinite is during combustion where it burns readily. 

Inertinite rich particles may have a longer burn out time compared with vitrinite but much of the 

difference appears to be due to the tendency of inertinite to occur as larger fragments. 

It has been shown that inertinite changes reflectance markedly during coalification. This is 

presumably associated with major chemical changes and many of these may relate to the 

elimination of the more loosely bonded forms of oxygen. At higher levels of maturation or rank, 

the greater abundance of strongly bonded oxygen is probably the reason why inertinite does not 

develop such a strongly preferred orientation within the molecular groupings. As a result, inertinite 

shows much lower levels of bireflectance than vitrinite (or liptinite) and this property is a major 

distinguishing feature within the anthracitic range. 

Smith and Cook (1981) point out that the mean reflectance of macerals of the inertinite group shows 

a systematic relationship to that of vitrinite. For coals, vitrinite is always present and vitrinite 

reflectance provides a better measure of rank compared with inertinite reflectance. As Smith and 

Cook point out, provided a diverse population of inertinite is present, inertinite reflectance can be 

used as a measure of rank. The laboratory of the author routinely reports inertinite reflectance of 

samples that contain small vitrinite populations as a method of checking the vitrinite reflectance 

data. Unpublished work with Geotrack International, shows that in a large number of basin studies, 

the inertinite reflectance data is extremely useful for sections where vitrinite is rare or absent. 

Inertinite probably generates catagenic methane at high levels of maturation but contributes only 

minor amounts of liquid hydrocarbons at lower levels of maturation. However, it may be a major 

source of early formed carbon dioxide. This could play a significant role in relation to migration of 

hydrocarbons in the range of vitrinite reflectance from about 0.45% to 0.7%. 

2.3.3.3.2 FUSINITE 

Fusinite chiefly represents charred material resulting from forest fires. A small proportion is 

present as primary fusinite. This latter is derived from tissues that naturally contain strongly 

bonded oxygen. Fusinite has a high reflectance but the reflectance of fusinite in brown coals is 

much less than that in higher rank coals. In the anthracitic range, the maximum reflectance of 

fusinite is "overtaken" by that of vitrinite. Fusinite shows little or no bireflectance and this property 

is an important distinguishing feature in high rank coals. Cell structures are commonly well 

preserved in fusinite. Fusinite tends to be prominent in distal marine Mesozoic sections. 

2.3.3.3.3 SEMIFUSINITE 

Semifusinite represents either partially charred material from forest fires or humic material that has 

become partially oxidized by biochemical activity. This last may include mouldering processes 

where the temperature of the peat is raised due to biochemical activity. In common with fusinite, 

semifusinite may have well preserved cell structures. Semifusinite ranges in reflectance from 

marginally above that of the co-existing vitrinite to that of fusinite. 

2.3.3.3.4 INERTODETRINITE


Inertodetrinite represents small fragments derived by the physical degradation of other types of 

inertinite. Most is probably derived from fusinite and semifusinite. It shows a similar range or 

reflectance to the full semifusinite to fusinite range. Inertodetrinite is widely distributed in coals 

and dom. Some of the smaller fragments may be windborn. 

2.3.3.3.5 MACRINITE 

Macrinite represents humic material that has first become gelified and then fusinized in the peat 

stage. It is an important component of many Carboniferous and some Permian coals but is not a 

major component of most Mesozoic coals and is absent or rare in Tertiary coals. 

2.3.3.3.6 MICRINITE 

The origin and even the nature of micrinite have been in dispute. It occurs as near sub-microscopic 

specks within macerals such as vitrinite, sporinite and bituminite. It shows some similarities to the 

bright specks resulting from small holes within the vitrinite component termed porigelinite and 

some workers claim that micrinite also represents holes. Another view is that it represents a carbon 

rich residue from disproportionation reactions that yield micrinite and hydrocarbons. Micrinite has 

been noted to form during hydrous pyrolysis experiments. Micrinite tends to be widely dispersed in 

coals. Its volumetric estimation can be difficult, except where it occurs as massive pods, because of 

its small size. 

Most commonly it is argued that micrinite is a response to rank change, but it does occur in large 

amounts in some very low rank coals, so that apparently it can have an origin from a different set of 

processes. 

2.3.3.3.7 FUNGINITE 

The term funginite refers to material of fungal origin and in older literature was termed sclerotinite. 

Much, or all, of the so-called sclerotinite described for Palaeozoic coals was either fusinized resin 

(macrinite) or poorly preserved semifusinite. Fungal sclerotinite is present only in Tertiary coals 

although material of fungal origin must be present in the older coals. It can only be presumed that 

in the older coals, fungal tissues cannot be distinguished from vitrinite (or possibly from some of 

the semifusinite). It is also possible that some material of fungal origin is included in vitrinite for 

Tertiary coals. 

In Tertiary coals, a variety of forms are present as sclerotinite; sclerotia (resting spores), 

teleutospores, mycorrhizomes (symbiotic associations of fungal tissue with higher plant roots) and 

stromata (fungal fruiting bodies). For coals of about 0.5% vitrinite reflectance, sclerotinite 

reflectance is about 0.9%. In higher rank coals, the reflectance of the sclerotinite is very close to 

that of the vitrinite and in the semi-anthracites is distinguishable mainly because of lower 

bireflectance compared with vitrinite. 

In very low rank coals, the lumens of the sclerotinite are typically empty or, less commonly, 

impregnated with material similar to corpocollinite. In coals of vitrinite reflectance greater than 

about 0.45%, the lumens of sclerotinite commonly include strongly fluorescing material similar to 

resinite or exsudatinite within the cell lumens. This may have affinities with bitumen but could 

represent migrated resinite. Fluorescing cell contents commonly give a streaming yellow oil cut in 

fluorescence mode but appear to be a secondary feature. 

2.3.3.3.8 SECRETINITE


This term was introduced to apply to the fusinised resin-related entities that had formed the bulk of 

the material referred to sclerotinite for Palaeozoic coals. It consists of rounded bodies, commonly 

with very high polishing relief and reflectance. The best documented origin is from resin rodlets 

that have become fusinised. 

2.3.4 MICROLITHOTYPES 

The term microlithotype was developed to permit the designation of rock types within coal that are 

at a microscopic scale and their definition is based on maceral percentages. All macerals have a 

suffix "-inite" and microlithotypes have the suffix "-ite". Thus, layers greater than 0.05 mm in 

thickness and consisting of greater than 95% vitrinite are termed vitrite. Bimaceral (clarite, durite 

and vitrinertite) and trimaceral (duroclarite and clarodurite) microlithotypes have names that are 

derived from lithotypes rather than macerals. 

In Palaeozoic coals, a wide range of microlithotypes can be present, but vitrite, clarite, durite and 

inertite are generally the most abundant components. A major difference between Carboniferous 

and Gondwana coals relates to the presence of inertinite as durite in the former and as inertite in the 

latter. Within Tertiary coals, the microlithotypes commonly present in significant proportions are 

vitrite and clarite (liptinite greater than 5% and inertinite less than 5%) except for microlithotypes 

containing mineral matter. Use of microlithotype terms assists by indicating the ratio of 

telovitrinite (preferentially associated with vitrite) to detrovitrinite (preferentially associated with 

clarite) and the amount of liptinite present. However, these distinctions can commonly be made 

more directly by using maceral analyses. 

Reproducibility of microlithotype analyses is generally not as good as that for maceral analyses and 

since about 1980, they tend to have fallen into disuse. However, inter-laboratory ring analyses 

showed that experienced analysts could obtain reproducible results. While point counting using a 20 

point ocular is extremely slow, the method using visual estimate of each field called selon la ligne 

can give reliable data and is much faster than point counting macerals. This appears a paradox at 

first sight as the decisions to be made with microlithotype analyses is inherently more difficult than 

that for maceral analysis. The explanation is that with maceral analysis you need to wait for the 

stage to stop to see exactly what is under the cross-hair, whereas with microlithotype analysis the 

layer to be named may be clear before the stage has stopped completely. 

2.4. COAL RANK - PHYSICO-CHEMICAL COALIFICATION 

2.4.1 PROCESSES ASSOCIATED WITH RANK CHANGE 

The gross effect of a rise in rank or the level of organic maturation is an increase in the carbon 

content of the organic matter and a decrease in the content of other elements, especially oxygen and 

hydrogen. 

The factors operative in this second stage of coalification are essentially:- 

1. Temperature - temperatures even below 60°C can have marked effects over long periods of 

time. 

2. Time - the rate constants of many reactions are such that time is an important factor in 

determining the level of coalification.


3. Pressure - this is probably an inhibiting factor since many of the reactions have gaseous or 

liquid decomposition products (C02 , CH4 , H20 and liquid hydrocarbons). Hydrostatic 

pressure tends to slow down the rates of reaction. The rate of diffusion of gaseous products 

away from the organic matter is an important additional factor which is linked in part to the 

pressure regime and the pressure regime itself can be partly controlled by the rate of diffusion 

of the products of coalification. 

4. Catalytic and inhibiting effects either of other organic material or of inorganic materials, 

particularly some of the clay minerals. 

Like coalification, carbonization is a process of alteration of organic matter leading to an increase in 

carbon content and a decrease in oxygen and hydrogen content. However, the process of 

carbonization is essentially different to coalification. Carbonization occurs if organic matter is 

heated rapidly - hours or days to reach 500°C, for example, instead of the millions of years required 

for coalification. The response of organic matter to carbonization is variable depending upon the 

nature of the material involved and its rank at the time of carbonization. For humic material with < 

80% total carbon, carbonization results in a char. Chars have a relatively high oxygen to hydrogen 

ratio, with much of the oxygen cross-linked so that they cannot be graphitized by further heating. 

Humic material with 80 - 91.5%C becomes plastic at about 400°C and at 500°C yields a semi-coke 

which can be graphitized by further heating. Anthracitic rank humic organic matter (total carbon > 

91.5%) can also be graphitized by heating but does not develop a plastic stage. 

Coalified material has different properties from carbonized organic matter. Coalification and 

carbonization should not be used as equivalent terms. Optical properties can be used to distinguish 

the products of coalification from those of carbonization. Cokes show a very distinctive mottled 

appearance due to the presence of a mosaic of graphitic domains. Chars and contact altered organic 

matter that has not been coked typically show anomalously low levels of bireflectance. 

2.4.2 MATURATION CONCEPT 

Oil-like hydrocarbons are not present in significant amounts in sediments or organic matter close to 

the sediment fluid interface. They develop as a result of thermal breakdown of some of the 

compounds originally present in the sediment when formation temperatures increase due to the 

build up of overlying (usually younger but similar considerations apply if additional cover is due to 

overthrusting) sequences. According to the thermogenic-organic theory of hydrocarbon origin, the 

hydrocarbons are largely of thermogenic origin. The extent to which the original organic matter is 

changed by heat acting over long periods of time under confining pressure is said to be the level of 

maturation. 

The maturation concept is basically similar to the rank concept in coal studies. The main difference 

is that in coal studies the emphasis is on the solid residue whereas in petroleum studies the emphasis 

is on the fluid products. However, most assessments of the level of maturation rely on properties 

measured on solid phases. Accepting that there is a different emphasis, the terms rank and level of 

maturation can be used interchangeably.


The changes associated with physico-chemical coalification and maturation may be 

diagrammatically represented as follows: 

TABLE 2.8. PHYSICO-CHEMICAL COALIFICATION – RANK CHANGE 

INITIAL MATERIAL PROCESS RESPONSE 

BROWN COAL 

IMMATURE DISPERSED 

ORGANIC MATTER 

COMPOUND 

GROUPS 

COALIFICATION HIGHER RANK COALS, 

ANTHRACITE, GRAPHITE 

MATURE DISPERSED ORGANIC 

MATTER 

METHANE AND OTHER FLUIDS 

Aromatization, loss of 

functional groups, loss 

of oxygen preferentially 

and then hydrogen 

Rise in carbon content, loss of 

oxygen and then hydrogen 

The main changes in humic material are the loss of O, H, N and an increase in C, the 

degree of aromaticity, removal of alkyl groups, functional groups, cracking of aliphatic 

molecules, dehydration and decarboxylation. Changes in the more aliphatic and 

naphthenic components (mostly found within liptinite) are small until the middle of the 

bituminous rank range when evolution of long chain hydrocarbons, demethylation and 

aromatisation occur. 

Note: The coalification/maturation processes result in solid organic residues containing a higher 

content of carbon compared with their precursors and fluid products. The general form of these 

reactions is termed disproportionation. Although the solid residues have higher densities and 

therefore smaller volumes, this is more than offset by the volumes of the fluids that are produced. In 

physicochemical terms, pressure can therefore be expected to inhibit coalification or maturation 

processes. In natural systems, it is difficult to demonstrate the nature of the effects of pressure but 

some unusual features appear to be associated with overpressured zones. 

2.4.3. ORGANIC PETROLOGICAL METHODS 

Organic petrology permits determination of the type and abundance of the organic matter occurring 

as discrete particles at the same time that rank or level of organic maturation is assessed. 

Maturation level is normally and most easily assessed from vitrinite reflectance but the fluorescence 

properties of both liptinite and vitrinite can also be used as an indicator of rank. Providing that the 

vitrinite is correctly identified, vitrinite reflectance provides the most direct and precise method of 

rank assessment for most samples. In the absence of discrete organic matter, it is possible in some 

instances to use the fluorescence characteristics of the mineral matter to give a general assessment 

of the level of maturation. 

Organic matter type and abundance can be used to determine coal properties and the source 

potential of sections intersected during petroleum exploration. In combination with the maturation


level, they are used to assess the probable liquids and gas yields to date. It is conventionally 

believed that because liptinite has the highest H/C ratio, it is also the major source of petroleum 

liquids. In many cases, vitrinite and inertinite are more abundant in sedimentary rocks than 

liptinite. If most of the organic matter is vitrinite, its greater abundance may outweigh the higher 

specific yield of the liptinite. This situation appears to obtain many source rock sequences 

containing coal measures. Even within the liptinite group, the specific yield of oil-like compounds 

may vary by a factor of at least five. Thus, accurate identification of the individual macerals is 

essential. The vitrinite reflectance range over which the various macerals yield liquids differs, so 

that maceral composition determines, in part, the timing of liquids generation as well as the amount 

of liquids yielded. The oil industry, generally, does not yet require organic matter type analyses at 

the level of specificity and precision which they actually need. This is slowly changing. 

Organic petrology methods are useful at most stages of the exploration cycle for both coal and 

hydrocarbons. In frontier basins they are used to define the overall prospectivity and to try to 

delimit the most prospective horizons (source rocks) and to determine the areas where source rocks 

will be mature enough to have generated significant amounts of oil (so-called source kitchens). 

During the drilling phase, geochemical data are needed both to test the original prognosis for the 

wells and to generate a new set of data to give a firmer basis to predictions. If a wildcat well is a 

discovery, it is desirable to learn more accurately the source of the oil or gas so that the search for 

similar plays can be appropriately directed. 

If the exploration well is unsuccessful, organic petrological data can indicate the type and rank of 

any coals that might be present in nearby areas and are needed to determine if source rock quantity, 

quality or level of maturation is a main or contributory cause of the lack of a discovery. Organic 

petrology will indicate if trace amounts of coal, oil or gas are present in the section have the 

potential for economic discoveries. At more mature stages of exploration, it should be possible to 

map variables that can be used to predict the amount of coal present or the amounts of oil or gas 

which at given part of the sequence should have generated. 

Some workers tend to consider techniques as being competitive. A number of techniques 

(including some which have been pushed very strongly as panaceas for all problems) have proved 

to be of limited value. However the source rock maturation process and oil and gas systems are so 

complex that a wide range of techniques is needed to obtain an adequate understanding of the 

processes and responses (see, for example, Jones et al, 1984 and Murchison et al, 1985). Thus, for 

the most part, techniques should be regarded as complementary rather than competitive. As far as 

possible, organic petrology should be linked in with other studies both more general aspects such as 

stratigraphy and tectonic history and specialist studies, for example, apatite fission track analysis.

2.4.4. VITRINITE REFLECTANCE 


2.4.4.1 OPTICAL PROPERTIES OF VITRINITE AND THEIR INFLUENCE ON 

MEASUREMENTS 

Reflectance is considered as the percentage of light reflected from a polished surface when the 

incident beam is perpendicular to the polished surface. Especially in the case of anisotropic 

materials, reflectance changes with the angle of incidence. 

In practice, the light beam that is measured comprises a semicone, the angle of which is controlled 

by the aperture of the objective lens and the working distance of the lens. Different microscopes 

and lenses give different angles of cones. The reflectance is measured by comparing the intensity 

of light reflected from an unknown with that reflected by the same optical set-up from a standard of 

known reflectance. This feature of the technique largely eliminates errors associated with the 

optical characteristics of the microscope. Some small effect probably remain, because the standards 

are commonly isotropic whereas the vitrinite is anisotropic. Effects due to this difference are likely 

to be very small and have never been reported in detail. 

In normal practice, oil immersion lenses of about 40x to 50x nominal magnification and a numerical 

aperture of about 0.8 are used. For measurement, a Berek prism illuminator, or more recently a 

Smith illuminator, is used to give low glare. Glare should be further reduced by stopping down the 

field to about 10% of the full field. Measuring stop size should be small to permit mineral 

inclusions to be avoided. The image of the back projected measuring spot on the sample should be 

about 0.001 or 0.002 mm square. 

The formula from which reflectance is calculated is: 

I u 

I s 

xR s (1) 

where Iu and Is are the intensities of light measured for the unknown (in this case the vitrinite) and 

the standard, respectively and Rs is the reflectance of the standard. The reflectance of the standard 

is generally calculated from its refractive index using equation (1). In order to calculate the 

reflectance correctly, the refractive index must be known accurately and the refractive index of the 

immersion oil must also be know. Immersion oils have a significant coefficient of change in 

refractive index with temperature and show some spectral dispersion. The refractive index for the 

immersion oil should be 1.518 at 546 nm (the mercury green line). This refractive index is 

normally given at a temperature of 23 o C. Within a temperature range of about 21 o C to 25 o C effects 

of temperature change are small but beyond that range start to become significant. A surprisingly


Table 2.4. Diagram to illustrate the ISO coal classification 11760-2005 related to a diagram used in Pinheiro and Cook (2005). 

Bed Moist → VR → 

75% 35% 0.4 0.5 0.6 1.0 1.4 2.0 3.0 4.0 6.0 

C B A D C B A C B A 

Tertiary, Kalimantan, R vmax 0.48% Permian, Australia, 1.05% R vmax Cretaceous, Angola, 2.03%, R vmax 

LOW-RANK COAL MEDIUM-RANK COAL HIGH-RANK COAL 

LIGNITE SUB-BIT 

BITUMINOUS ANTHRACITE 

ORTHO/ META/ 

PARA ORTHO META PER PARA ORTHO META 

Weich Hart /Glanzbraunkohle 

PF steam PF steam PF steam Steam/PCI PCI/SOFT PRIME BLEND Possible PCI Graphitizable 

COKING COKING LV/pci 

carbons 

Terms from the German DIN system have been shown for low rank coals, Weichbraunkohle, Hartbraunkohle and Glanzbraunkohle.


Table 2.5 - Low, Medium and High Rank coals 

LOW RANK COALS 

Bed Moist → VR% → 

75% 35% 0.4 0.5 

R vmax 0.37% Permian 0.38% Tertiary Scotland 0.46% Tertiary, Kalimantan 

C B A 

LOW-RANK COAL 

LIGNITE SUB-BIT 

ORTHO META 

STEAM STEAM STEAM 

MEDIUM, RANK COALS 

0.5 VR% 0.6 1.0 1.4 2.0 

R vmax 0.54%, Tertiary 

0.64% Carboniferous, UK 1.08% Carboniferous, USA 1.74% Jurassic, Australia 

D C B A 

MEDIUM-RANK COAL 

BITUMINOUS 

PARA ORTHO META PER 

STEAM \ PCI 

HIGH RANK COALS 

PCI/SOFT COKING PRIME COKING BLEND LV/PCI 

2.0 VR% 3.0 4.0 

2.16% Tertiary, W Canada 3.16% Roseneath, Cooper Basin, Perm. 

Australia, pxp 

5.87% Permian W Papua, pxp- 

partially crossed polars 

C B A 

HIGH-RANK COAL 

ANTHRACITE 

PARA ORTHO META


large number of laboratories around the World do not have effective temperature control for 

photometer units and many laboratories in countries in high latitudes commonly take measurements 

with temperature below 20 o C. As noted below, it is not possible to correct for the errors associated 

with incorrect oil RI values unless the refractive index and the absorptive index of the vitrinite are 

known. Cook and Murchison (1977) present data that show errors are minimised if standards that 

have a reflectance slightly higher than that of the unknown are used as the primary standard for 

calibration, but this is not always possible. 

Vitrinite is anisotropic. The anisotropy is not due to the presence of a crystalline structure as is the 

case for minerals but to the presence of preferentially oriented domains that have been termed 

micelles. This type of anisotropy is termed form anisotropy and is similar in origin to the properties 

shown by liquid crystals. 

Vitrinite approximates the optical properties of a unixial negative material. The reflectance 

indicating surface is analogous with the optical indicatrix that is studied for more transparent 

materials. With opaque substances, construction of the wave envelope within the material is much 

more difficult to represent because the properties are defined by tensors. However, if radii are 

drawn corresponding to the reflectances that obtain for any given direction within the substance, 

this provides a model of the optical behaviour that can be used in much the same way as an optical 

indicatrix can be used. 

Graphite is uniaxial negative and is crystalline. Most vitrinites are optically analogous with 

graphite although the cause of the optical properties differs, especially at low ranks. An optically 

uniaxial negative indicating surface, is an ellipsoid of rotation with the plane of circular section 

corresponding with the maximum radius. Ellipsoids of rotation have the property that a section cut 

in any direction includes the radius that forms the plane of circular section. Thus, for unixial 

negative materials, all sections include the maximum reflectance. The section cut perpendicular to 

the plane of circular section both true maximum and true minimum reflectances. The plane of 

circular section itself shows only the maximum reflectance. All other sections (oblique sections) 

show the maximum and an apparent minimum reflectance. 

The mean radius for an ellipsoid of rotation is twice the value for the plane of circular section plus 

the value for radius perpendicular to the plane of circular section divided by three. For a negative 

uniaxial reflectance indicating surface, this corresponds with 

( 2Rmax 

� Rmin 

) 

3 

Cook et al (1972) and Stone and Cook (1979) have shown that biaxial or irregular properties can be 

present within the indicating surface. Irregular properties cannot occur with structure anisotropy 

but appear to be possible where form anisotropy is present. Where biaxial characteristics are 

present, the two planes of circular section are present, and these intersect at variable angles. 

Typically these planes are close to where the plane of circular section would have been and the 

(2)


material is then biaxial negative. For biaxial materials, Rmax, Rint and Rmin are present. If the angle 

of intersection between the planes of circular section is small, the intermediate reflectance Rint is 

close to the value of Rmax. 

If angle of intersection of the planes of circular section that includes the Rmax exceeds 90 o , the 

material resembles biaxial positive characteristics in its properties. Levine and Davis (1984) have 

reported this for a coal within the Pennsylvania anthracite belt. However, in their study, they 

prepared only three sections, one parallel with bedding and two others mutually at 90 o that were 

perpendicular to bedding. Stone and Cook (1979) used at least four to six sections and found that 

indicating surfaces were irregular rather than simply being biaxial. This adds additional complexity 

and it would be useful if the work on the anthracites was repeated using a greater number of 

sections. 

Normally, the extent to which indicating surfaces depart from the uniaxial model is so small that it 

can be ignored. Errors caused by biaxial properties are likely to be small compared with other 

possible sources of error for coals of bituminous or brown coal rank. Within anthracites, more 

attention to the nature of the indicating surface is required. For bituminous coals, it is probable that 

the greatest significance of biaxial properties. 

2.4.4.2 RELATIONSHIP OF REFLECTANCE TO OTHER OPTICAL PROPERTIES 

The relationship of reflectance to refractive index for transparent materials is given by the Fresnel 

equation: 

R = 

( ns � nm) 

( ns � n ) 

m 

2 

2 (3) 

Where ns is the refractive index of the unknown substance and nm is the refractive index of the 

immersion medium. For air lenses the refractive index of the immersion medium is 1. For all other 

immersion media, the refractive index of the immersion medium must be known. The form of the 

numerator in the equation means that small errors in either refractive index have a marked effect on 

the calculated value for reflectance. 

This equation is used for calculating the reflectance of most of the standards that are used but 

should not be used for coal macerals. The value for R that is obtained is scaled from 0 to 1, the 

more normal mode of expression is obtained by multiplying this value by 100. 

For absorbing materials, the Beers equation should be used. This is similar to the Fresnel equation 

but contains additional terms: 

R = 

m 

2 2 

s � 

2 

s 

m 

2 2 2 

s � s 

( ns �n ) �n 

( ns �n ) �n 

(4)


The refractive index terms are identical with those in the Fresnel equation and �s represents the 

absorptive index of the substance. The Beers equation contains two unknowns and thus it is 

impossible to calculate the refractive index from the reflectance measured in a single immersion 

medium. Most studies do not involve the use of the refractive index of the unknown substance. 

However, this characteristic means that it is impossible to correct the reflectance obtained 

experimentally for non standard conditions such as a different immersion medium or the correct 

immersion medium but with non-standard temperatures leading to a different refractive index for 

the immersion medium. 

If reflectances are known for two immersion media it is possible to calculate both the refractive 

index and the absorptive index for the unknown. In the following formulae it is assumed that the 

two media used are air (n =1) and immersion oil (the standard has been set at 1.518): 

and 

or 

ns = 

where ks = ns�s. 

( n 2 

o � n 

2 

a )/ 2 

1 � R 

no[ o 1 � R 

] � na[ a ] 

1 � Ro 1� 

Ra ks = Ra n ( s �na ) 

2 

�( ns�na ) 

2 

n 2 

s ( 1� 

Ra ) 

ks = Ro n 2 2 

( s � no ) �( ns�no ) 

n 2 

s ( 1 � Ro ) 

Cook and Murchison (1977) presented extensive data on the relative errors that occur in the 

calculation of n and � for various errors in determination of reflectance. These calculations can also 

be used to estimate the relative errors in R from errors in assumptions about various optical 

parameters involved in the Beers equation (equation 4). 

The data presented by Cook and Murchison (1977) show clearly that not only must standards have 

known reflectances (generally calculated from equation 3, the Fresnel equation), but the oil must 

also have a known refractive index. Immersion oils vary in refractive index with temperature and 

the wavelength at which it is measured. Unless equations 5, 6 and 7 can be solved, corrections for 

incorrect values of noil cannot be made. 

Jakeman and Cook (1978) present detailed information about the variation in refractive index and � 

for a range of coals. In the course of this work, it became clear that most laboratories have never 

determined the refractive index of the immersion oil used. The refractometer (Abbé) that is 

(5) 

(6) 

(7)


commonly available can only be used for the sodium “D” line, and the Pulfrich refractometer that is 

required for other wavelengths is a rare piece of equipment. Jakeman and Cook (1978) discovered 

that no such instrument existed in Australia and had to use a spectrometer. 

2.4.5. TECHNIQUES FOR MEASURING VITRINITE REFLECTANCE 

2.4.5.1 GENERAL 

For given methods of sample preparation, the main variations in the methods of measuring vitrinite 

reflectance relate to: 

1. immersion medium used, some older work reports measurements with “air” lenses but most data 

relate to the use of oil immersion lenses, and the oil became standardised at n = 1.518 at 546 nm by 

about 1970; 

2. to the use of plane polarized light to measure the maximum reflectance or of weakly polarized 

light to measure approximately the average of mean maximum vitrinite reflectance and the apparent 

minimum vitrinite reflectance (Rvmin) in each field; 

3. whether or not the stage is rotated to find the maximum value; and 

4. techniques of field selection. 

Variations also exist in data interpretation. Presentation of histograms is common but it is not 

always clear how these are used. Original data listings are not, commonly made available even 

though recalculations cannot be made without such data. 

2.4.5.2 USE OF VARIOUS IMMERSION MEDIA 

Most of the older Russian literature is based on determinations in air. This appears to the due to the 

low quality of oil immersion lenses available in Russia until recently. It may also have been due to 

lack of sensitivity in photometers. 

Corrections from measurements in air to an oil basis cannot be made without either determining n 

and � (presumably by also making measurements in oil!). Figure 1 in Cook and Murchison (1977) 

gives an indication of the relationship between air and oil reflectances. Jakeman and Cook provide 

data that can be used to estimate the refractive index of the vitrinite, permitting a better estimate to 

be made. 

Diessel has drawn attention to the value of making reflectance measurements in water immersion. 

This permits fluorescence measurements with a minimum of interaction with the coal to be made at 

the same time as the reflectance measurements are made. Based on experimental data, he has found 

a best-fit relationship for the relationship between oil and water reflectances to be: 

Rw �109 . �143 

. Ro (8)


where Rw and Ro are reflectances for water and oil immersion respectively. The form of this 

equation in comparison with equations 3 through 7 indicates that this is a descriptive fit rather than 

an analytical fit. Where unusual combinations on n and � are present, this type of estimation may 

be considerably in error. 

2.4.5.3 PROPERTIES MEASURED 

The main methods used and the optical properties measured are set out in Table 2.4. Corrections 

between the various properties listed in Table 2.4 are general approximations. As bireflectance has 

been shown by Jones et al (1984) to be provincial, it is important to be certain that any correction 

factors are appropriate to the coals under study. 

PROPERTY 

MEASURED 

Maximum 

reflectance 

Reflectance of 

sample is measured 

in the orientation of 

the grain found 

during scanning of 

the sample 

OPTICAL 

PATH 

ROTATION OF STAGE 

Polar Rotation to find maximum, 

preferably both maxima and 

the average is that parameter 

used 

Rmax 

Polar No rotation of stage Not always 

distinguished from 

random reflectance 

Random reflectance No polar No rotation of stage 

Table 2.9. Properties measured for vitrinite reflectance. 

2.4.5.3.1 MEAN MAXIMUM REFLECTANCE 

Rrandom or Rm 

Provided vitrinite is close to uniaxial in character, the Rmax value will be found in any section of 

the vitrinite. If the beam of incident light is plane polarized, as the stage is rotated the maximum 

value should be encountered twice and, 90 o from the maximum values, a minimum value is found. 

In the general case this will be an apparent minimum and it lies between the true Rmin and the 

Rmax. Both maximum and minimum values may be recorded but the maximum value is normally 

the only value used. 

The polar should be inserted with the polarization direction at an angle of 45 o to the horizontal cross 

hair in the ocular. This orientation produces minimum ellipticity of the polarization during 

reflections through the illumination system of the microscope.


The various layers of vitrinite within a coal or other type of sediment typically show some variation 

in reflectance. Therefore it is necessary to measure a number of fields in order to obtain a 

representative value for the mean. It is has been common practice in Europe to measure 100 fields 

and this has been repeated in a number of standards. However, no statistical study appears to have 

been undertaken in establishing this number. It is also the case that the variation with the random 

reflectance method used in Europe is greater than that for maximum reflectance and with maximum 

reflectance, in essence two measurements are obtained for each field. 

The SAA Working Group did undertake such a study after members had commented that the 

precision of the mean appeared to approach that of reading the standard after 20 to 25 readings. 

Results were presented in the order in which they were obtained and analysed statistically and it 

was shown that the running mean had converged on the final mean for a batch of 100 readings after 

about 20 readings had been made. The Working Group recommended a minimum of 30 values be 

obtained. 

Normally, the maximum reflectance is either in the plane of the bedding or is very close to that 

plane. If oriented blocks are measured, the true minimum values can also be obtained. Murchison 

(pers comm, 1970) has suggested a method of estimating the minimum value from randomly 

oriented grain mounts. The procedure suggested involves measurement of 100 maxima and minima. 

The greatest 5% of values for Rmax-Rmin are then used as an estimator for the bireflectance. Rmin 

is then taken as Rmax minus the bireflectance. Bireflectance can be used as an indicator of the 

coalification history of coals. The simplest use is the detection of proximal contact alteration where 

bireflectances are anomalously low, except in the case of natural cokes. Jones et al (1984) have 

shown differences in bireflectances between coalfields in the UK and Germany and it is possible 

that some of these differences may correlate with the behaviour of coals in processes such as 

carbonization. 

At low rank, bireflectance is low and the difference between maximum reflectance and other 

measurements is small. As rank increases, bireflectance tends to increase and the difference 

between maximum reflectance and other measures also increases. It was common practice in 

Germany to ignore bireflectance for coals with vitrinite reflectance


Measurements may be made on all of the vitrinite found in the sample, or on specific maceral subgroups, 

or even individual macerals. This last is most common where very low rank coals are 

measured and the corpocollinite may provide the most stable indicator of rank. Brown et al (1964) 

suggested that restriction of measurements to vitrinite A (in effect the component now referred to as 

telovitrinite) would increase precision and this is now followed in some procedures where 

measurements are restricted to collotelinite. 

2.4.5.3.2 RANDOM MEASUREMENTS BUT WITH POLAR 

Some laboratories use a polar in the light train but do not rotate the stage in order to find the 

maxima. The results are usually reported as Rrandom but compared with the more normal method 

of measuring this show a higher dispersion of values. This is because the values recorded can range 

from the true maximum to the true minimum. 

2.4.5.3.3 RANDOM REFLECTANCE 

This is measured without a polar in the light train. The stage is not rotated. Values obtained should 

range from close to the true maximum (sections parallel with bedding) to half the sum of the true 

maximum and the true minimum (for sections perpendicular to the bedding). The range is probably 

slightly greater because the opaque illuminators all impart a degree of polarization to the beam of 

incident light. 

The variation obtained is not as great as that in the method outlined in 7.3.2 but is greater than that 

for maximum reflectance. Variation due to difference in grain orientation increases markedly with 

increasing rank and is severe for coals within the anthracitic range of rank. 

A number of estimators have been published for converting random reflectance to maximum 

reflectance or vice versa. Neavel et al (1981) on the basis of studies on US coals that: 

% Rmax � 1106% . Rrand � 0. 024 (8) 

Diessel and McHugh (1986) suggest for Australian coals: 

% Rmax � 107% . Rrand � 0. 01 (9) 

Authors of these formulae seldom present the error measures for the correlations found. 

Additionally, while the correlations exist within the data used, they may prove to be poor predictors 

for data sets from different geological provinces. 

2.4.6. HISTOGRAMS 

Histograms are a convenient method of presenting reflectance data. They can be used to examine 

type variation within the vitrinite of single coals and can be used to detect blends of coals of 

different ranks. The usual interval used to present histograms is 0.05%, sometimes referred to as a


half V-step. It is important to note that where a class interval of 0.05% is used, single coals may be 

bimodal. With some coals of Mesozoic age, trimodal histograms are not uncommon from a single 

oriented block of coal. This property is a function of the extent of type variation within the vitrinite. 

Complete separation of the modes should not occur with single coals. 

The number of readings necessary to provide a stable histogram is much greater than that needed to 

obtain a stable mean. With a range of about 0.25% in vitrinite being common, 100 readings is only 

marginally sufficient to provide stable numbers in each histogram category. For blends, the number 

of readings is much greater again, and may exceed 250 depending upon the number of reflectance 

categories distinguished. 

Histograms appear to have been used first in 1961 by Cook in Brown et al (1964) to demonstrate 

type variations within vitrinite. Dow (1977) has argued that histograms can be used as primary 

method of identifying first generation vitrinite. In practice, it is not possible to identify zones 

within a histogram as representing any given maceral in the absence of qualitative data on the 

morphological characteristics of the fields measured. The main situation where histograms are of 

real value is where cavings populations represent a problem. Even here it is desirable to pick 

cavings on the basis of lithological associations rather than on an arbitrary pick of where the 

envelope of the indigenous population appears to end. 

Identification of the population of first generation vitrinite is of critical importance and should be 

made at the time of measurement rather than from a data review. Thus, a small number of 

reflectance measurements made on undoubted first generation vitrinite by examining whole rock 

samples yields more accurate data than large numbers of poorly characterized measurements made 

on organic matter concentrates. 

Hunt (1979, p468) comments on the rise of standard deviation with reflectance. However, his data 

probably relate to the use of random reflectance data measured without the use of a polar on organic 

matter concentrates. Mean maximum vitrinite reflectance values on whole rock samples are much 

more precise than Rrand at higher ranks and while the standard deviation of mean maximum 

vitrinite reflectance does increase with rank it does not show the logarithmic increase shown by 

Hunt. 

A few workers float coal grains from cutting samples and measure the floated grains. The floated 

grains may be cavings or in some cases mud additive or other types of contaminant. This procedure 

is not recommended. 

2.4.7 UNUSUAL TYPE EFFECTS 

The presence of bitumens or alginite can yield anomalously low vitrinite reflectance values and 

most other measures of coalification are also affected. Careful choice of a full suite of samples can 

usually minimize or eliminate these problems. Cook and Sherwood (1988, 1990) have shown that 

most other techniques also give anomalous data where high contents of alginite are present and 

similar anomalies can be expected for bitumen rich samples. For example, in a suite of oil shales, 

T max correlates best with H/C atomic ratio and therefore with alginite content rather than with the


level of maturation. Petrographic techniques are probably the most robust for this type of sample, 

because experienced petrologists are able to note the presence of the alginite or bitumen and steps 

can then be taken to find samples which are free of these components. Recent claims concerning 

the ability of fluorescence methods to provide a method of correcting for anomalously low vitrinite 

reflectances remain to be fully tested. 

Within brown coals, type variation can exercise a considerable effect on vitrinite reflectance. Most 

commonly this is thought of as being variation between collotelinite or its precursors and 

collodetrinite and its precursors. However, some major variations in wood types are present within 

some coals especially those of Mesozoic or Tertiary age. A note should be made where unusual 

tissue types are present. The root tissues of some species and most leaf tissues tend to have 

reflectances that are anomalously low. 

Vitrinite reflectance data can be used to produce well profiles or maps and fence diagrams. Maps 

may be of reflectances at a nominated stratigraphic horizon or the depth to a specified reflectance 

level. It is also possible to construct three-dimensional reflectance surfaces though the amount of 

data required to yield reliable three dimensional surfaces is much greater than that required for twodimensional 

mapping of reflectance. 

2.5 CARBONIZATION 

“Normal” coalification takes place under confining pressure and at relatively slow rates of heating. 

Where unusually high heating rates occur due to the presence of an adjacent igneous mass 

coalification processes are accelerated. The properties of organic matter that has been affected by 

contact alteration differ from those associated with normal coalification. The products of contact 

alteration show some affinities with the products of artificial carbonization as in the processes of 

charring, coking and calcining. 

Low rank organic matter becomes charred and tends to retain textural features associated with low 

rank coals even though reflectances may be up to about 3.0%. Charred materials have low 

bireflectance and high polishing hardness. These properties can be useful to distinguish material 

that is a response to contact alteration as opposed to the products of “normal” or regional 

coalification. 

Medium rank organic matter can take on the properties of cokes. Where alteration takes place under 

shallow cover, the natural cokes can develop vesicles, but if it occurs under thick cover, natural 

cokes lack vesicles. Natural cokes can be isotropic but more typically show a distinct to pronounced 

mosaic structure (Figures 2.2 and 2.3). Natural cokes show extremely high bireflectances.


FIGURE 2.1 PLATES OF COALS AND THE CONVERSION TO ARTIFICIAL SEMI-COKES. 

MOST OF THE TEXTURES FOUND IN THE TWO RIGHT HAND PHOTOGRAPHS CAN BE 

FOUND IN NATURAL COKES. 

Exsudatinite is a response to coalification through the low rank part of the oil window. With normal 

coalification, it appears that exsudatinite is lost at a vitrinite reflectance of about 0.70 to 0.80%. 

Meta-exsudatinite has been recognised but it appears to be confined to sections that have undergone 

contact alteration. The Bukit Assam coal in S Sumatera contains meta-exsudatinite with a 

reflectance of about 2.4% in the semi-anthracitic coal. The lower rank surrounding coal contains 

“normal” exsudatinite with low reflectance and distinct fluorescence, but unpublished work (T. 

Gilbert and the present author) showed that extracts of the exsudatinite contain 1-dienes, usually 

taken as an indicator of pyrolysis. 

Figure 2.4 shows a medium rank Permian coal from NSW that contains abundant meta-exsudatinite 

with a reflectance markedly above that of the associated vitrinite – 1,24% compared with 0.92%. 

Although the coal is of moderate rank, the presence of the meta-exsudatinite is considered evidence 

of some contact alteration. Similar examples have been found of meta-exsudatinite in the Tertiary 

of Gippsland Basin and it occurs only in sections with igneous intrusions.


FIGURE 2.2. Mesophase development in natural bitumen, E Jawa, Eocene. Contact alteration is due 

to hot gas streaming as there are no igneous rocks in the section drilled. the spherical masses are 

mesophase (Rmax 2.8%) Embedded within a mesostasis of material (Rmax 2.0%) that would all 

be converted to coke mesophase had heating continued. Field width 0.22 MM. 

FIGURE 2.3. Natural coke. Little Limestone coal, Visean, Carboniferous, Northumberland, UK.. 

Semicoke maximum reflectance 2.5%, even medium mosaic. Field width 0.18 mm.


If contact alteration occurs once coals have reached the top end of the range for coking coals, the 

altered coals have very high bireflectances. 

FIGURE 2.4. MEDIUM RANK PERMIAN COAL, NSW. THE VITRINITE HAS A 

REFLECTANCE OF 0.92%. VEINS OF META-EXSUDATINITE (R=-1.24%) ARE PRESENT 

INDICATING THAT THE SECTION HAS UNDERGONE CONTACT ALTERATION. FIELD 

WIDTH 0.22MM.

2.5. BIBLIOGRAPHY AND REFERENCES 


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Appendix. Glossary 


Bioclast - fragmentary material derived from plants or animals. Phytoclast refers specifically to plant derived material 

and is related to the term phyteral proposed by G.H. Cady for plant fragments. 

Bitumen - (a) Geological/mineralogical usage. A generic term applied to natural inflammable substances of variable 

colour hardness, and volatility, composed principally of a mixture of hydrocarbons substantially free from 

oxygenated bodies. Petroleums, asphalts, natural mineral waxes, and asphaltites are all considered bitumens. 

(b) Geochemical usage. The fraction of organic matter in rocks which is soluble in mild solvent such as carbon 

tetrachloride. In this usage the organic matter is then divided into soluble (bitumen) and insoluble (kerogen) 

fractions. 

The two usages in general refer to different kinds of occurrences of oil-related organic matter. Most bitumens have 

a high solubility in weak organic solvents but some are relatively insoluble. See also kerogen and organic matter. 

Bituminous - term for coals of medium rank (Mean maximum vitrinite reflectance 0.6% to 2.0%). Coals of this rank 

typically have a high yield of bitumens when treated with mild organic solvents and have been termed bituminogels 

as opposed to coals of lower rank that have been termed hydrogels. 

Brown coal - brown to black coal of low rank (Mean maximum vitrinite reflectance


average compositions. Rock-Eval data are also used to attempt to determine kerogen type. Early attempts to use 

HI and OI have largely been abandoned because it is recognized that the OI value is very unreliable. An alternative 

has been to plot HI against Tmax . This is commonly used to estimate kerogen type and vitrinite reflectance but the 

results are indicative rather than definitive. 

Liptinite - maceral group term including hydrogen-rich organic matter derived from spore and pollen coats, cuticles, parts 

of bark tissue, resins and algal remains. Liptinite has a higher content of aliphatic compounds as compared with 

the other maceral groups. The use of the stem “lip” relates to the term lipids. This is unfortunate because most 

liptinite is not related to the group of compounds included in the term lipid. The earlier term was “exinite” derived 

from “exine” and related mainly to sporinite and cutinite but not to other macerals such as resinite and suberinite. 

Thus, the name for this maceral group was changed from one unsuitable word to another unsuitable word. 

Lignite - A brownish-black coal intermediate in coalification between peat and sub-bituminous coal (US terminology). 

Lopatin model - coalification/maturation model based on the assumption that the rate of coalification rate doubles for 

every 10 o C rise in temperature and is linearly related to the time during which a unit occupies any given 

temperature interval. The model produces a function known as the time/temperature integral which has been 

correlated with vitrinite reflectance. The basic model does not take account of differing rates of reaction for 

various types of organic matter or of changes which occur in reaction types over the range of maturation levels. 

Functions to take account of these variations have been included in some modifications of the basic model. 

Macerals - microscopically resolvable organic constituents comprising coal. The term was introduced by Marie C. 

Stopes in 1935 and is intended to show the analogy between macerals in coals and minerals in other types of rocks. 

Maturation - a concept used as a measure of the extent to which the original organic matter within a sediment has been 

transformed into oil or gas or both. The further concepts of oil and gas windows are an essential part of maturation 

theory. 

Organic matter - the total amount of organic matter within a rock. Organic matter occurs as discrete entities (macerals), 

true solution within pore water, colloidal solution, as free liquid hydrocarbons and as bitumens which are absorbed 

on to or in mineral grains. The vast majority of organic matter in most rocks occurs as macerals. The term kerogen 

is used by some authors to imply total content of organic matter but its use should be restricted to that fraction 

which is insoluble in mild solvents. 

Organic matter type - a measure of the types of organic entities present. Type can be measured in terms of maceral 

composition, entities seen in transmitted light, or using chemical composition, in terms of kerogen type. 

Organic sulphur - sulphur that is chemically bound to organic molecules. It is determined by measuring total sulphur and 

subtracting the sum of pyritic sulphur + sulphate sulphur. 

Palynomorph - microscopic, resistant-walled organic body found in palynologic maceration residues; a palynologic study 

object. Palynomorphs include pollen, spores of many sorts, acritarchs, chitinozoans, dinoflagellate thecae and 

cysts, colonial algae with organic tests, and other acid-insoluble microfossils. 

Rank - term originating in the commercial side of the coal industry and now used as a measure of the degree of 

physico-chemical coalification. Rank change is a response to elevated temperatures acting over long periods of 

time. Pressure may have a slight retarding effect upon the rates of reactions. Coalification to the ranks of 

bituminous coal and semianthracite occurs at temperatures generally below 200oC. It is essentially a metamorphic 

process but, in part, occurs over the range of P,T conditions associated with processes referred to as diagenesis. 

Rank is essentially the same concept as level of organic maturation. Common measures of rank are vitrinite 

reflectance, total carbon (dry mineral matter free basis). Volatile matter yield is also used but is unreliable where 

the yield is above about 30%.


Reflected white light - the form of illumination used for vitrinite reflectance measurements and for general observations 

of the humic macerals (vitrinite and inertinite). Some resolution of mineral matter phases is also possible. The 

light source is typically a quartz halogen lamp. A weak blue filter is required to give normal "white" colour 

balance. 

Resinite - a liptinite maceral derived from higher plant resins. Resins occur in a number of different settings including 

wood, leaves and surrounding damage to woody tissue. The purpose of most resins appears to make plant tissues 

less edible by insects and fungi. Many terpanes are derived from resins but hydrocarbons derived from resin have 

very wide range of structures including bicyclic and monocyclic naphthenic molecules and a range of polycyclic 

aromatic compounds. Resinite is thought to become oil mature at low levels of rank but to give either a naphthenic 

or aromatic oil. 

Rvmax - see vitrinite reflectance. 

Sporinite - a liptinite maceral formed from the exines or, less commonly, the entines of spores and pollens from plants. 

Sporinite is derived largely from sporopollenin which has a naphthenic structure and as such is unlikely to 

contribute significantly to the paraffinic compounds that are dominant in most oils. 

Telovitrinite - vitrinite derived from woody or leaf tissue which has retained much of its original morphology. 

Telovitrinite is orthohydrous to subhydrous. See also detrovitrinite. 

Terrestrial - material deposited on "dry" land. In terms of organic matter it is usually taken to distinguish between higher 

plant material and algal sourced organic matter. However, some higher plants (such as mangroves) live in standing 

water and those such as Zostera (a sea grass) cannot live in areas which are not permanently flooded and some 

algae live in areas which are predominantly dry. The term is, nevertheless commonly used to make a distinction 

between different floral assemblages. 

Terrigenous - material derived from the land surface. In terms of organic matter this includes both higher plants and algal 

sourced organic matter from lakes. 

UV light - in the context of fluorescence mode microscopy, the 365 nanometre line of mercury, usually obtained using a 

UG1 excitation filter. 

Vitrinite - maceral group derived from woody, leaf or related tissue. During early diagenesis the precursors of vitrinite 

become extensively hydrolysed and repolymerize as humic and fulvic acids. During maturation water is expelled 

and a turbostratic structure develops within the aromatic part of the vitrinite. Gelification is variable during the 

peat stage but as maturation proceeds gelification becomes more intense leading to a massive structure. Vitrinite 

occurs in coals and as dom. In most coals vitrinite acts as a mesostasis within which the other macerals occur. At 

low ranks, vitrinite is easily deformed and has the properties of a rheid. Rheidity is lost at anthracitic rank. 

Vitrinite is usually the most abundant maceral group in coals but Tertiary coals are unusual in having very high 

proportions of vitrinite. Vitrinite classification was revised in 1994 and the new system is referred to as “Vitrinite 

Classification, ICCP System 1994” 

Vitrinite reflectance - the amount of light reflected by a plane polished surface of vitrinite when illuminated with a beam 

of light with a ray path which is perpendicular to the surface. In practice the light usually is in the form of a 

semicone. Standard measurement conditions are in immersion oil of refractive index 1.518 and at a wavelength of 

546 nanometres (mercury green line). Immersion oils only have an RI of 1.518 at 23oC +/-2oC. If polarized light 

is not used the reflectance is commonly referred to as Rm. If polarized light is used the maximum reflectance 

should be found in any section regardless of orientation as vitrinite approximates the behaviour of a negative 

uniaxial material. Mean maximum reflectance is calculated from the means of the maxima obtained and is referred 

to as Rvmax. Rvmax should not be confused with the maximum of the range of reading found for any given 

sample. Use of polarized light reduces the dispersion of readings as compared with Rm, as Rm for any given field 

in a grain mount of randomly oriented grains, is approximately given by Rmax + Rapparent min)/2 and Rm for the 

sample is given by 2Rmax + Rmin /3. Thus, dispersion of values due to the bireflectance increases the dispersion


caused by type variation. Some vitrinite clearly depart from a uniaxial indicating surface but Rint is usually close to 

Rmax so that in practice measuring Rvmax gives a stable rank and maturation sensitive measure.

APPENDICES. 


TABLE A2.1. MAJOR CONSIDERATIONS IN RELATION TO VITRINITE 

REFLECTANCE 

SAMPLE REQUIREMENTS 

SAMPLE PREPARATION 

OPTICAL PARAMETERS MEASURED 

PRECISION 

MEASUREMENT PROCEDURE 

INFORMATION IN VITRINITE REFLECTANCE DATA 

LIMITATIONS AND COMPLICATIONS 

A. LIMITATIONS 

B. COMPLICATIONS 

1. REFLECTANCE BELOW "TREND" 

2. REFLECTANCE ABOVE "TREND"


TABLE A2.2. SAMPLE REQUIREMENTS FOR VITRINITE REFLECTANCE 

TYPICAL - 20 GMS OF SAMPLE 

MEASUREMENTS CAN BE MADE ON 

A. HAND PICKED FRAGMENTS - MINIMUM SIZE APPROX 10 MILLIGRAMS 

B. GRAINS OF VITRINITE WITHIN SAMPLE - MINIMUM WEIGHT 

FOR 25 MEASUREMENTS, APPROX 3X10 -15 GRAMMMES. 

PRECISION 

PRECISION RISES WITH:- 

A. SAMPLE SIZE 

B. SAMPLE REPRESENTIVITY 

COAL SAMPLES TEND TO YIELD MORE PRECISE DATA THAN DISPERSED ORGANIC 

MATTER BECAUSE TYPE VARIATION CAN BE MORE ACCURATELY IDENTIFIED. 

AT 25 READINGS FOR MOST SAMPLES THE STANDARD ERROR OF THE MEAN IS LESS 

THAN THE STANDARD ERROR OF MEASURING THE STANDARDS AND ADDITIONAL 

"PRECISION" FOR THE MEAN IS SPURIOUS. 

AT 100 READINGS, THE HISTOGRAM CATEGORIES ARE NOT "STABLE". IF STABLE 

HISTOGRAMS ARE REQUIRED, BETWEEN 100 AND 200 READINGS ARE REQUIRED. 

IN GENERAL, MORE INFORMATION IS OBTAINED BY NOTING VITRINITE TYPE AND 

ASSOCIATIONS THAN BY COMPUTING HISTOGRAMS. HISTOGRAMS HAVE THEIR MAIN 

VALUE IN DEFINING THE PROPERTIES OF POPULATIONS THAT HAVE ALREADY BEEN 

CHARACTERIZED ON OTHER GROUNDS (MORPHOLOGY AND ASSOCIATIONS).


TABLE A2.3. METHODS OF MEASUREMENT 

SAMPLE PREPARATION 

A. WHOLE ROCK SAMPLES AND COALS - TEXTURAL INFORMATION PRESERVED. SOME 

DIFFICULTY IN LOCATING ORGANIC MATTER IN "LEAN SAMPLES. EASIER TO IDENTIFY 

MACERALS WHEN MATERIAL IS FOUND. 

B. DEMINERALIZED SAMPLES PREPARED AS STREW MOUNTS - TEXTURAL INFORMATION 

LOST AND THE MORE READILY FLOATED MATERIALS SUCH AS LIPTINITE. MACERALS 

MUCH MORE DIFFICULT TO IDENTIFY. READINGS EASIER TO OBTAIN BUT NOT ALWAYS 

CLEAR WHAT IS BEING MEASURED. 

OPTICAL PARAMETERS 

A. WITH POLARIZER IN LIGHT TRAIN (IN 45 o ) POSITION. 

A1. WITH ROTATION OF STAGE R MAX IS MEASURED 

A2. WITHOUT ROTATION RRANDOM. 

B. WITH NO POLARIZER IN LIGHT TRAIN (THE ILLUMINATORS WILL ALWAYS GIVE SOME 

ELLIPTICAL POLARIZATION OF THE INCIDENT BEAM). RANDOM REFLECTANCE IS 

MEASURED - Rm. . Note: the Rm obtained without a polarizer is not the same as that 

obtained with a polarizer in the light train. 

Rvmax SHOWS LESS DISPERSION AS COMPARED WITH Rm FOR ANY GIVEN SAMPLE. THE 

DISPERSION FOR Rm TENDS TO INCREASE MORE MARKEDLY THAN THAT FOR Rvmax AT 

HIGHER REFLECTANCES. USE OF THE POLAR PERMITS MEASUREMENT OF 

BIREFLECTANCE. THIS HELPS IN DISTINGUISHING VITRINITE (MODERATE TO HIGH 

BIREFLECTANCE) FROM INERTINITE (LOW BIREFLECTANCE) AND ASSISTS IN PICKING 

THERMALLY ALTERED SEQUENCES (USUALLY ANOMALOUSLY LOW BIREFLECTANCE).

MEAN 


TABLE A2.4. INFORMATION IN REFLECTANCE DATA 

DISPERSION - STANDARD DEVIATION OR RANGE (OR BOTH) 

HISTOGRAM - THIS GENERALLY HAS LITTLE UTILITY WITHOUT A DESCRIPTION OF 

THE VITRINITE MEASURED 

DESCRIPTIONS SHOULD ALSO BE PROVIDED OF: 

1. ROCK TYPE(S) 

2. FOR CUTTINGS, CONTAMINANTS 

3. MACERAL DESCRIPTIONS 

4. A RECORD OF THE TYPE OF VITRINITE FOR EACH FIELD MEASURED 

5. SPECIFIC RECORD OF THE PRESENCE OF BITUMENS AND OIL CUT AND OF THE 

MODE OF OCCURRENCE OF BITUMENS


TABLE A2.5. LATER DEVELOPMENTS 

1. DETECTORS 

A. PHOTON COUNTERS (FIRST INTRODUCED ABOUT 1978 BY US STEEL) 

B. DIODE DETECTORS 

C. CHARGE COUPLED DEVICES - CAMERA PHOTOMETERS 

CAMERA PHOTOMETERS MAY WORK IN SPOT MODE (CRAIC SYSTEM) OR IN FIELD MODE 

(HILGERS) SYSTEM. 

2. AUTOMATED SYSTEMS 

A. AUTOMATIC STAGE SYSTEMS WITH VARIOUS METHODS OF "IDENTIFYING" 

VITRINITE" - ONLY SUITABLE FOR COALS 

B. IMAGE ANALYSERS WORKING IN FIELD MODE AND WITH FULL PIXEL COUNT 

(TYPICALLY 425,000+ PER FIELD). PLUMBICON TUBE GIVES POTENTIALLY 

ABOUT 256 GREY LEVELS. IN PRACTICE DETECTION LEVELS ARE 

STRONGLY AFFECTED BY SURFACE CHARACTERISTICS AND EVEN FOR 

COALS DETECTION IS AFFECTED BY BOUNDARY EFFECTS AND BY 

POLISHING DEFECTS. 

C. DIGITAL CAMERA – PIXEL COUNTS GENERALLY HELD AT ABOUT 1.3 

MEGAPIXELS. 

3. OPTICS – DISTINCT IMPROVEMENTS. BUT RELIANCE ON ELECTRONICS CAN MAKE 

THEM LESS RELIABLE THAT PURELY MECHANICAL SYSTEMS. 

4. DATA ACQUISITION 

A. INTERFACES AND EDITING PRESENTATION ROUTINES. 

5. ACCREDITATION OF ANALYSTS BY ICCP.

A. LIMITATIONS 


TABLE A2.6. LIMITATIONS AND COMPLICATIONS 

1. HIGHER PLANTS ARE LARGELY DEVONIAN AND LATER. IN PRACTICE GRAPTOLITES 

CAN BE USED FOR MOST OF THE LOWER PALAEOZOIC AND ALGINITE AND BITUMENS 

HAVE BEEN USED SUCCESSFULLY FOR SOME CAMBRIAN AND PRECAMBRIAN 

SEQUENCES. 

2. BARREN SEQUENCE OR RELATIVELY BARREN SEQUENCES 

a. RED BEDS - NOT ALWAYS BARREN, CHECK. 

b. SOME LIMESTONES ESPECIALLY REEF LIMESTONES, BUT THERE MAY BE 

BITUMENS PRESENT AND STYLOLITES SHOW CONCENTRATIONS OF 

ORGANIC MATTER 

c. SOME SANDSTONES 

d. DISTAL MARINE SEQUENCES - MAINLY INERTINITE BUT THIS GIVES AN 

INDICATION OF THE HIGHEST Rvmax POSSIBLE. 

3. SYSTEMATIC DIFFERENCES ARE PRESENT BETWEEN VITRINITE REFLECTANCE DATA 

FROM COALS AND FROM DOM IN THE INTERSEAM STRATA. 

4. SIDEWALL CORES ARE TYPICALLY SHOT ON GAMMA HIGHS AND USUALLY SHOW MUCH 

LOWER VITRINITE REFLECTANCE VALUES COMPARED WITH SEDIMENTS WITH LOWER 

GAMMA READINGS AND COMPARED WITH COALS.

TABLE A2.6. COMPLICATIONS 


COMPARED WITH THE "AVERAGE" TREND (THE TREND FOR A CONTINUOUS SEQUENCE 

OF COAL SEAMS) Rvmax MAY BE EITHER ABOVE OR BELOW TREND. THIS TENDENCY CAN 

BE ESTIMATED FROM OBSERVATIONS MADE DURING THE MEASUREMENT SEQUENCE 

A. BELOW TREND 

READINGS WITH BELOW-TREND VALUES ARE COMMONLY WRITTEN UP AS SUPPRESSED 

VITRINITE. THIS IS UNFORTUNATE BECAUSE LOW READINGS CAN BE DUE TO AT LEAST 6 

ENTIRELY DIFFERENT CAUSES, EACH REQUIRING DIFFERENT CONSIDERATION. 

1. VITRINITE TYPE - DETROVITRINITE, PRESENCE OF SUBERIN-TYPE TISSUE OR RESINS, 

MESOPHYLL TISSUE 

2. EDAPHIC CONDITIONS - EARLY PEAT CONDITIONS CAN INFLUENCE REFLECTANCE, 

SEVERE EFFECTS ARE UNCOMMON 

3. PRESENCE OF ORGANIC SULPHUR (CHANGES ELECTRON DENSITY OF AROMATIC 

STRUCTURES) 

4. PRESENCE OF ALGINITE 

5. PRESENCE OF BITUMENS WITH PERMEATING MODE OF OCCURRENCE 

6. IMPREGNATION WITH OIL 

NOTE: IF BITUMINITE OR SUBERINITE IS INCORRECTLY REPORTED AS VITRINITE, 

RESULTS WILL BE MUCH TOO LOW. 

IT MAY BE POSSIBLE TO CORRECT FOR SOME OF THESE EFFECTS – IN ORDER: 

1. AVOID THE LOW REFLECTING TISSUES AND REPORT THEM SEPARATELY. 

2. COMMONLY A PART OF A COAL SEAM WILL SHOW “NORMAL” REFLECTANCES, WITH 

THE LOW REFLECTANCES BEING RESTRICTED TO THE TOP OR THE BASE. 

3. USUALLY NOT POSSIBLE TO MAKE A CORRECTION FOR THIS EFFECT. 

4. IF SAMPLES ARE AVAILABLE WITH VARYING ALGINITE CONTENTS, A CROSS PLOT CAN 

BE MADE. EXTRAPOLATION BACK TO ZERO ALGINITE GIVES A GOOD APPROXIMATION TO 

A “NORMAL” VALUE. 

5. DIFFICULT TO CORRECT, BUT USUALLY SOME ZONES WILL BE LESS AFFECTED BY 

BITUMENS. 

6. AGAIN, SEARCH FOR SAMPLES LACKING STRONG OIL CUT. 

SOME ALGINITE-RICH SAMPLES CONTAIN TWO POPULATIONS REFERABLE TO VITRINITE. 

WHERE THIS IS THE CASE THE HIGHER REFLECTING POPULATION APPEARS TO SHOW 

LITTLE INFLUENCE FROM THE PRESENCE OF ALGINITE.

TABLE A2.6. COMPLICATIONS (CONTINUED) 

B. ABOVE TREND 


1. REWORKING - MOST LIKELY IN SOME LACUSTRINE AND MOST MARINE SEQUENCES; 

DETECTED BY POLISHING RELIEF, GRAIN SHAPE AND FORM OF BOUNDARIES AND 

TEXTURAL RELATIONSHIPS 

2. ANOMALOUS VITRINITE IN SANDSTONE - SOME VITRINITES HAVE HIGH REFLECTANCE 

BUT ARE DISTINCTIVE BY THE PATCHY APPEARANCE, CELL STRUCTURE AND HIGH 

BIREFLECTANCE 

3. DOMINANCE OF HIGHLY REFLECTING TELOVITRINITE 

NOTES 

A. REWORKED VITRINITE IS MUCH LESS COMMON AN OCCURRENCE THAN COULD BE 

CONCLUDED FROM SOME SETS OF RESULTS. IF A HIGH READING IS OBTAINED, THE 

MOST LIKELY CAUSE IS THAT IT REPRESENTS INERTINITE NOT REWORKED COAL. 

NEVERTHELESS REWORKED MATERIAL IS IMPORTANT IN SOME SECTIONS. 

B. THE RELATIONSHIP OF EACH READING TO THE LIKELY "TREND" VALUE CAN BE 

ESTIMATED AT THE TIME OF MEASUREMENT BUT CANNOT BE DETERMINED FROM A 

HISTOGRAM IN THE ABSENCE OF ADDITIONAL INFORMATION.


TABLE A2.7. REPRODUCIBILITY DATA FOR SIX COALS 

SAMPLE # 237 52 140 191 141 270 

GROUP STANDARD DEVIATIONS 0.035 0.041 0.052 0.033 0.034 0.04 

MMSD - MEAN MULTIPLE OF THE STANDARD DEVIATIONS [(X-XBAR)/SD] FOR 

35 ANALYSTS: 0.733 – very close to theoretical value 

MEAN STANDARD DEVIATION (6 samples, 35 analysts): 0.039 

APPROXIMATE AVERAGE ERROR LEVEL MEASURE (MMSD*MEAN SD) FOR 

ALL ANALYSTS: � 0.0286% 

NUMBER OF ANALYSTS HAVING AVERAGE ERRORS WITHIN 0.039% ABSOLUTE OF THE 

GROUP MEANS: 31 

APPROXIMATE AVERAGE ERROR LEVEL FOR ACCEPTABLE DATA SETS: � 0.0257% 

APRIL 2011

R Rrand - Universidade do Porto

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